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Gas & Electric Furnace Troubleshooting Simplified

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Below we have listed some common gas and electric furnace troubleshooing Problems and Solutions. I hope this will help you troubleshoot your furnace, solve your problem and save you money! Please contact us anytime if you have questions: Our email address is: We have online parts programs where we can look up the parts for the following furnace models: Amana, American Standard, Trane, Bryant, Carrier, Goodman, ICP (Heil, Tempstar Comfortmaker), Janitrol, Ruud, Rheem, and York furnaces.

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Troubleshooting Gas & Electric Furnaces

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*Please remember to turn off all electrical power and gas to your HVAC system when troubleshooting or working on HVAC equipment. We most certainly do not want to see anyone get hurt or damage their equipment! We have a good testing meter for sale on the following page: Please click to see a real good HVAC testing meter.

Please click on the picture below to see a furnace troubleshooting flow chart. Please click on the following link if you would like to see a printable PDF furnace troubleshooting flow chart: furnace troubleshooting flow chart This should help you troubleshoot to see what is wrong with your furnace.

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Would you like to see Videos on Furnace Repair?

click here if you would like to see a video/videos on how to replace your
ignitor and do other heating and air conditioning repairs. Hvacrepairguy has
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Below we have a YouTube video on gas furnace troubleshooting made by hvacrepairguy. Thank You hvacrepairguy! I hope this video will help you solve your furnace problems. If you have any questions please feel free to email us at: or respond in the comments section near the bottom of this page. We hope you have a blessed day! Steve & Barbara Arnold

Below we have listed some of the most common furnace problems with suggestions on what to look for and how to repair the problem.

Problem: One of the most common furnace problems that I see is when the furnace hot surface ignitor will not glow. If a furnace has a bad ignitor, loose wire connections, open limit switch, open rollout switch, open pressure switch or bad control board. This is what you might see in the furnace sequence of operation:

1. Thermostat calls for heat when you turn up the thermostat.
You should fist check to make sure you are getting 24 to 28 volts AC between the W (white) and C (com) terminals on your control board.
*Make sure furnace blower door safety switch is pressed in when testing. If your control board has a fuse on it make sure the low voltage fuse is not blown. You might have to temporarily tape the blower door safety switch closed for temporary testing. If the fuse is blown on the control board nothing will happen. If the fuse is blown you might have a short in the low voltage thermostat wires. Check to make sure wires are not pinched anywhere.

2. Draft inducer motor starts. If draft inducer does not start then you either have a thermostat problem, thermostat wiring problem, loose wire connection, transformer problem, bad draft inducer relay on the control board or a draft inducer problem. Please make sure you can spin the draft inducer wheel freely. Sometimes if the draft inducer sits for a long time (like over summer) without operating the draft inducer wheel can become tight.

3. Pressure switch attached by a small plastic or rubber tube to the draft inducer senses the negative pressure produced by the draft inducer and closes.
You should have 24 volts to ground across both terminals on the pressure switch.
If pressure switch is not closed with draft inducer running check for a stopped up vent or a stopped up condensate drain line if you have a condensing furnace.

4. Limit Switch and rollout switch/switches should all be closed. Press in on the reset button in the center of each rollout switch to make sure each rollout has been reset. You should have 24 to 28 volts from each terminal to ground. On most furnaces the ignitor will not glow unless all the safety controls (limit, rollout switch/switches, pressure switch) are closed. If a limit or rollout switch is open then you might have an over heating problem and a possible dangerous condition. If the Limit or rollout continues to trip I would strongly recommend calling an HVAC service company to check your furnace out.

5. Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound. If you hear a hissing gas sound with no gas ignition then more than likely either the ignitor is broken or the relay on the control board that sends power to the ignitor is broken. If the ignitor did not glow, the flame sensor (a small metal probe about 1/8″ in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the hissing sounds stops with no ignition of gas to heat your home. Your furnace will shut down, and try ignition again. Most of the time after three tries the furnace will and go into a lock out condition until you turn your power switch back off and on again.

You might need a new ignitor, rollout switch, limit switch, pressure switch or control board. We sell hot surface ignitors on the following page. Please click here for furnace hot surface ignitors. We sell 56 different ignitors. Please send your furnace make and model number if you would like for us to look up the ignitor for your furnace. If you have a Bryant or Carrier furnace we will need the product number. If you have a Rheem or Ruud we will need both model number and serial number. Our email address is:

Solution in an Emergency Situation. An Emergency situation would be a situation where your furnace ignitor goes out in the middle of the night, on the weekend or holiday. It is Super cold outside and you need to get heat from your furnace to protect your family and the pipes from freezing. Here is a link to a YouTube Video which shows how to manually light a furnace when the ignitor fails. I only provide this link because I do not want to see anyone be cold when they could actually have heat in the home. Changes in the video that I would make would be to: (1) use a long wooden match instead of the lighter. (2) Make sure the match is burning when the draft inducer comes on. You must make sure the match is sitting in front of the burners before the gas valve opens. The worst mistake would be to allow gas to come into the furnace and then apply the match. This could produce a  mini-explosion or fire! The match needs to be burning before the gas valve opens. Please click here if you would like to see a YouTube Video that shows how to Manually Light a Gas Furnace when you have a bad igniter. This video was made by Chris Swain.

Disclaimer: Arnold’s Service Company, Inc. assumes no liability for any incidental, consequential or other liability from the use of this information. All risks and damages, incidental or otherwise, arising from the use or misuse of the information contained herein are entirely the responsibility of the user. Although careful precaution has been taken in the preparation of this website’s information, we assume no responsibility for omissions or errors.

: Your furnace will not ignite the gas to produce heat for your home. When a furnace has a bad ignitor what I see most of the time is the following sequence of operation:

1. Thermostat calls for heat.

2. Draft inducer motor starts.

3. Pressure switch attached by a small plastic or rubber tube senses the negative pressure produced by the draft inducer and closes.

4. Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound. The ignitor did not glow, the flame sensor (a small metal probe about 1/8″ in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the hissing sounds stops with no ignition of gas to heat your home. Your furnace shuts down and goes into a lock out condition until you turn your power switch back off and on again. Then the sequence starts all over again with no ignition of the gas.

You probably need to purchase and install a new ignitor. I would suggest that you inspect your ignitor closely for cracks. Make sure you do not touch the ignitor with your bare hands. If you do not visually see a crack, then you could have a furnace control board problem or a limit, rollout switch problem. Please see “limits, rollout switches & furnace control boards” further down on this page. The furnace’s control board might not be supplying the voltage to the ignitor. Please click here for our Furnace Control Boards Page. If your furnace lights and the gas stays on for 8 to 10 seconds, then shuts right back off, then you need to clean your flame sensor with light sand paper or steel wool. You might need a new flame sensor, but most of the time they can be cleaned an will work well after cleaning. Please see the pictures below to help you identify a flame sensor. Here is a link to our Furnace Flame Sensors Page.


Below are pictures to help you identify what a flame sensor and ignitor look like. On the top is a picture of three different types of flame sensors. On the bottom is a picture of a hot surface ignitor. Make sure you do not touch the gray glass part of the ignitor. If you do it will shorten the ignitors life.



Please click here for Our Furnace Flame Sensors Page.

Please Click Here for Our Furnace Ignitors Page

Problem: My furnace ignitor is going out too much!

Below we have listed some reasons why your furnace ignitor might be going out so often. We hope this will help you from having to replace your ignitor so often!

*Please remember to turn off all electrical power to your HVAC system when trouble shooting or working on HVAC equipment. We most certainly do not want to see anyone get hurt or damage their equipment!

Please Click Here to go to Our Furnace Ignitors Page

Below are listed some reasons that might cause your ignitor to go out prematurely:

1. Handling the ignitor improperly by touching the gray glass part.

2. Installing an ignitor that is not made for the furnace.

3. High home line voltage. Check your voltage to see that you are in the 110 to 125 volt

range. Anything over 125 volts is going to cause premature light bulb failure and furnace

ignitor failure. Call your electric company if you are getting high voltage in your home.

Your electric company should be able to place a transformer on your line to lower your line voltage.

4. Debris from the heat exchanger or bugs/spiders can get on
the ignitor while the furnace is not calling for heat and when there is a call
for heat the debris/bug can short the ignitor out. It is a good idea to keep
your furnace and heat exchanger clean so this does not happen.

5. The ignitors have just so many on off cycles in them.
The reasons listed

below concern the furnace cycling off and on too much. These
reasons if they occur, will also cause you to have a high heating bill.

1. Over-sized furnace. A furnace that is too large for you home cycles too much. If your furnace is sized properly on your coldest day the furnace should run almost continuously. Shutting off very few times. I went to an HVAC training meeting on energy conservation. The speaker said, “The inefficiency of a furnace is in the On, Off cycling.” He made this statement that on the coldest day your furnace should almost run continuously if sized properly.

2. A dirty filter or blower squirrel cage causes too much cycling. Your furnace will go off on high limit continuously because it is not getting enough airflow through the heat exchanger. The furnace goes off on high limit to keep from overheating the furnace and possibly causing a fire. This is why it is very important to keep those filters changed.

3. A dirty restricted air conditioning evaporator coil causes restricted airflow that causes too much cycling. Make sure your coil is not stopped up on the underneath side. I usually have to take off the coil end plates and use a vacuum cleaner and coil cleaner to get all the lint and dirt off. Make sure you clean in the direction the coil fins are running. If you do not, it will bend the fins over and cause more restrictions. A good tool to use is our air conditioner fin coil cleaning tool.

Please click here to go to our air conditioner fin comb tools page.

4. Improper thermostat heat anticipator setting. Look at your gas valve and see the amp draw. Set you thermostat’s anticipator setting to this amp draw plus one amp more. If your gas valve says, “.4 amps” then set your thermostat to “.5” amps. This will give you a little longer run time and a longer off time. If you have an electronic thermostat: Many of the electronic thermostats have temperature differential adjustments or like on the Honeywell thermostats have screws where you can adjust to make your furnace cycle a little longer.

Below we have a pictures on the left of a label off a White Rodger’s gas valve and on the right a Honeywell Round thermostat anticipator. The label shows that this White Rodgers gas valve model #38C03 Type 300 draws .23A or .23 amps. The anticipator shown in the picture on the right is set on .4 amps. If I were using this White Rodgers Gas Valve and the Honeywell Round thermostat I would set the anticipator one amp more than the gas valve draws, on .3 or a little past the.3. The little copper looking pointer can be moved to make your furnace stay on longer by using your finger to move the pointer. Again, you should look at your gas valve’s amp draw to determine your setting.



6. Too much gas pressure causing the furnace to overheat because too much heat is being produced. This causes the furnace to cycle too much on high limit. Does your furnace’s gas pressure sound like a jet when it is running? Your gas pressure on your gas valve might be set too high. This produces too many BTU’s or too much heat. I would recommend a HVAC technician adjust this problem. Turning the adjustment screw clockwise gives more pressure. Counter clockwise gives less gas pressure. If you attempt to adjust this yourself, do not adjust more than 1/4 turn clockwise or counter clockwise. Delayed ignition, blow back, and a mini explosion, could occur. Again, I would recommend an HVAC technician do this adjustment. Getting this adjustment right will save you gas utility costs, and wear and tear on your furnace in the long run.


Please Click Here if you would like to go to Our Furnace Ignitors Page

Please Click Here if you would like to go to our Electric Heating Repair Parts Page.

Pressure Switch, Limit, Roll out Switch or Furnace Control Board Problems?

Problem: My furnace’s ignitor does not glow? This could be a pressure switch, limit, roll out switch, or furnace control board problem.

I see this problem many times during the heating season here in Louisville, KY. When your thermostat calls for heat the draft inducer (please see pictures below) should start which creates a draft in your vent pipe. If your vent piping is open, the hole in your draft inducer is open (not clogged with debris or water) and your pressure switch is working properly, then pressure switch will close the connection between two wires and send a signal to the control board saying, “Yes it is OK to continue with the ignition process.”

draft_inducer_full-300x297Goodman-draft-inducer-with-text-300x300Above are pictures of a draft inducers showing where the pressure switch tube attaches. Pressure switch tubes sometimes attach on the top bottom or near the center of the draft inducer. These are just two of hundreds of different draft inducer designs. Some are metal and some are plastic. Most of the time draft inducers are plastic on 92% furnaces & metal on 80% furnaces. *Make sure the opening where the pressure switch tube is attached to the draft inducer is open. Sometimes a small wire can be used to reestablish the hole. Make sure your water drain on a 92% furnace is open. If too much water backs up into the draft inducer it will not allow the pressure switch to close.

Also, all of your limit controls and other safety devices must be closed (a closed circuit between the two connections) to allow the furnace ignitor to glow and start the ignition process. If there is a break down in the pressure switch or other limit safety controls the furnace, for your safety, will not proceed with the ignition sequence. The computer chip inside the board says, Wooooh!, something is wrong here! Most furnaces will try this sequence for a total of three times then lock out. On most furnaces the only way to get them out of lock out mode is to turn the switch (looks like a light switch) on the side of the furnace to off and then back on again.


Above is a picture of three different types of limit controls. The two on the

ends should reset automatically when the furnace cools down. The rollout

limit switch in the center has to be manually reset by pressing the button in

on the top. All limit controls are there for your safety. Never by-pass these.

How do you test a pressure switch and other limit controls? This is for people who are experienced with electrical equipment and the use of a Volt Ohm meter. *Please never by pass a pressure switch or limit control. The pressure switch and limit switches are there for your safety. In the top picture I am testing a rollout limit switch to see if it is good. You would test by setting your volt meter to “Volts AC” and test the rollout switch by placing one meter probe on one terminal of the rollout switch and your other meter probe to a good ground. Below I have the red probe touching the top terminal of the rollout switch and the black probe touching a ground (body) of the furnace. You can see the I am getting 25.85 volts which means the rollout is good on the top terminal. I would next test the bottom terminal of the rollout by touching the red meter probe to the bottom terminal on the rollout switch and the black terminal to ground. If I get 25.85 volts on the bottom terminal the rollout is good. If I do not get any voltage on the bottom terminal then the rollout has tripped and can be reset (if equipped) by pressing in on the little button or replaced. If your rollout switch is tripped you probably have a stopped up heat exchanger or a leaking heat exchanger. I would recommend calling in a service technician to find out why the rollout switch tripped. If you have an open limit control either the furnace has over heated or the limit has gone bad. Problems that would make a limit open up would be dirty filters, dirty evaporator coil causing a restriction in the air flow or a slow blower motor (check the capacitor on the blower motor to make sure it is good). A weak blower motor capacitor will cause the blower to run slow and eventually fail. Pressure switches, and limit switches can be tested with a meter in the same manner. With the furnace calling for heat you can test each of the terminals on the pressure switch to ground to make sure the pressure switch is closed. You should be getting between 24 to 28 volts from each terminal to ground if the pressure switch is closed. If the pressure switch is open you either have a stopped up vent, drain line (if you have a condensing furnace) or bad pressure switch. Below we have three pictures of pressure switches. The picture on the left shows the full view of one pressure switch. Please keep in mind there are many different types. The picture on the right shows the two terminals that you can use to test to see if the pressure switch is operating properly. The front terminal is burnt and discolored. This is a clue that this pressure switch has a problem. The picture on the bottom is a black Goodman, Janitrol plastic pressure switch.

Above pic shows me testing a rollout switch.
Above pic shows me testing a rollout switch.

Above pic shows me testing a rollout switch.



Above are two pictures of pressure switches. The pressure switch on the top came off a 92%

furnace. It has two connections for pressure tubing. One tube would go to the water collection

box and the other tube would go to the draft inducer. The switch on the bottom has a burnt front terminal.


Above is a picture of a Janitrol Goodman pressure switch.

How should you test to see if a pressure switch is operating properly?

Set your meter to volts AC, turn your furnace on so it is calling for heat. The draft inducer should start. There should be either two or three wires going into your pressure switch. Probe one lead of the pressure with one lead of your meter while touching the other lead of your meter to ground. Ground would be any bare metal part of your furnace. This must be bare metal. I always try to touch the other lead of my meter to the furnace’s switch box. If you have a two wire pressure switch you should be getting 24 or more volts between both leads to ground. By this I mean if you touch one terminal of the pressure switch with one lead of your meter, and touch the other lead of your meter to a ground, bare metal part of your furnace, you should get 24 or more volts (24 to 28 volts). If you do not get 24 or more volts with the furnace running then you have a pressure switch problem. Your vent could be stopped up, The tube that runs from your pressure switch to the draft inducer could be plugged up or the draft inducer hole could be plugged up. On high efficiency condensing furnaces the water drain line could be stopped up, causing a water back up and blockage in the pressure switch tube. I usually take the drain hose loose from the condensing furnace and use a wet vacuum to open the drain back up. I hope this will help you in troubleshooting your gas furnace pressure switch.

Problem: Draft inducer will not start, ignitor will not glow or gas valve will not open.

Solution: Any combination of the above problem or problems could be caused by a bad furnace control board. I always troubleshoot and test the least expensive parts first, such as the pressure switch, limit switch and rollout switches to make sure they are all closed and operating correctly before I go to the control board. First, and most important things to remember is turn your electrical power off to the furnace. Most control boards are located in the blower compartment. Many control boards have a fuse located on them to protect the board from getting burned up if you have a short to ground. The fuse is usually a 3 to 5 amp fuse similar to the fuses that you might find in a car’s fuse box. Please see picture below of the furnace control board:

Nordyne board 903106 instructions

If your fuse is blown you will want to check and see if any of the low voltage thermostat wires are touching the metal frame of the furnace or grounding out. Most of the time I see fuses that are blown from animals chewing through the thermostat wires and from the wires grounding out to the body of the furnace where the wires enter or exit the furnace. The vibration of the furnace over time sometimes wears through the wires insulation and causes a short to ground. I would try a new fuse first, then if the fuse blows again you are going to need to find out where the wires are shorting out. This can be quiet time consuming.

If your fuse is OK, tape your door safety switch shut so you can view the status LED light on the control board with the furnace power on. Please remember to turn the power back off before touching anything inside the furnace. I do not want to hear of anyone getting hurt or shocked! Turn your thermostat up so it is calling for heat. Let the furnace cycle and see if the Status LED flashes a code. The directions for reading the code are usually located on the furnace door. The code will usually tell you what is wrong with the furnace. Technology is amazing! Best of luck on repairing your furnace. Please remember to turn that power back off before touching anything.

Troubleshooting Electric Heat problems:

Problem: Electric heat will not come on or fan will not come on.

1. First and most important, Please make sure your electrical power is turned off before trying to repair or inspect any type of electrical appliance. I would recommend that you purchase an Volt Ohm meter for some of the troubleshooting procedures listed in this section. We have a real good Volt, Ohm, Amp testing meter on the following page: Please click here for a real good testing meter.

2. Inspect the inside of the air handler or electric furnace for burnt wires. I find this to be a major problem. Electric furnaces use lots of electricity. Any connections that are the least bit loose inside the furnace will cause a heat build up, arcing and eventually a completely burned off connection. Before long the entire wire will be burnt off. Please see picture (compliments from one of our nice customers) below of a burnt heat sequencer. You can see where the heat build up and arcing has caused the terminals to completely burn off the left side! This looks like a three stack sequencer, because of the divisions in the layers of the sequencer:


3. Check your breakers or fuses inside the air handler. Again, make sure your power is off. A good electrical tester multimeter would be nice to test your fuses. Many air handlers have fuses in them like the ones pictured below. You can remove these fuses and test them with a multimeter or if you do not have a multimeter, install new fuses to make sure they have not gone bad.


4. If you still are not getting electric heat then you should test your sequencers to make sure they are working. I made myself a tester so I could get portable 24 volts without having the furnace power turned on by using an old fan center connected to a junction box with alligator clips attached to the fan center. We sell new fan centers on our Please click here for fan centers.


Tester made from Fan Center.

Son’s 13 Tennis shoe propping up tester. Ha!

When 24 volts is applied across the two bottom connections on this sequencer you should get continuity (a closed circuit) between the two terminals the one on the left M1 and the one on the right M2. You should also have continuity between M3 & M4. This might take 30 to 90 seconds after the 24 volts is applied before you get the continuity. If you do not get continuity then you might want to purchase one of the sequencers we have for sale on the following page: Please click here to see the sequencers we sell. We have a real good Youtube Video below made by ACservicetech which explains how sequencers work. If you have any questions please email us anytime:

2 Stack Sequencer
2 Stack Sequencer


Below are links to some of my favorite sites for Heating, Air Conditioning repair and advice:

Please Click Here to go to our Electric Heating Repair Parts Page.

Please Click Here to Visit One of my favorite Websites for HVAC Troubleshooting & Repair: HVAC Talk.

Please click here for a glossary of electrical terms with examples and explanations. This is an excellent resource for understanding electrical terms.

Please click here for another great Website where people can talk about their HVAC problems and get answers!

This a link to one of my favorite sites for Heating, Air Conditioning repair and advice: Please click here for Building & Environmental Inspection, Testing, Diagnosis, Repair & Problem Prevention Advice.

Please Remember Safety First

Please read our disclaimer and safety related information below before attempting to do any

type of Heating or Air Conditioning Repair. We do not want to see anyone get hurt or shocked!

Thank You!

*Please always turn off all electrical power, and discharge the capacitor/capacitors (if working around capacitors) before attempting to inspect or repair any heating & air conditioning equipment. Check to make sure the electrical power is off with a reliable meter.

Disclaimer: Arnold’s Service Company, Inc. assumes no liability for any incidental, consequential or other liability from the use of this information. All risks and damages, incidental or otherwise, arising from the use or misuse of the information contained herein are entirely the responsibility of the user. Although careful precaution has been taken in the preparation of this website’s information, we assume no responsibility for omissions or errors.

Privacy Statement: Please click here to see our Privacy Policy page if you are interested. Arnold’s Service Company, Inc. is committed to protecting your privacy. Your personal information and email address will not be sold, rented or given to anyone. Your information will be used ONLY by Arnold’s Service Company, Inc. We promise you!

God Bless you all.

Sincerely, Steve & Barbara Arnold

11506 Seatonville Road

Louisville, KY. 40291


88 thoughts on “Gas & Electric Furnace Troubleshooting Simplified

  1. 2010 Coleman electric furnace for mobile home. It heats find & AC works fine. Problem is the fan keeps going even after desired temp is reached. Fan keeps going even when heat & ac is off on wall mounted temp display or control thing that you use to turn on/off for AC or heat. Had this replace 3 times & furnace repaired 3 times. Only way to turn off the fan is to bang on the furnace door panel a few times.
    Can you help?????

    1. Hi Tim! This sounds like you either have a sticking fan sequencer or if your unit does not use a sequencer to control the fan then you might have a sticking fan relay or control board. It would depend on finding out which control controls the fan motor then replace the sequencer, fan relay or control board with a new one. You will need to test with a volt meter to see which control is causing the fan to run all the time. If you would like for me to look up the part number for the relay, control board, etc. then please send your electric furnace’s air handler model number to me at I hope you can find the control that is causing your fan to stay on soon! Steve

  2. My gas furnace will not stay lit. When it calls for heat the inducer starts, the igniter glows, the gas comes on and ignites, stays on for 3 seconds and shuts off. I get a light code that says ignition error check ground. I replaced the flame sensor to be sure and checked my grounds which were good. What is the next step I should take? Thanks!

    1. Hi Wes! Please see the following post where I try to explain and answer the question you asked: If you need me to look up parts please send your furnace’s model number to our email address Thanks! Steve

  3. My very old electric furnace has began to mess up and I dont know why. It kicks on, the fan runs but the heat’s does not. You can disconnect the power and reconnect and the heat kit is on and starts heating. WhT could it be??
    Thanks in advance

    1. Hi Tim! More than likely you have a sequencer problem. We have a good post with two good Youtube videos that I hope you help you out on the following page: I would first recommend that you turn the power off to your furnace and check all wire connections to make sure they are good and tight and not burnt. When I was doing service on electric furnaces many times I would find burnt connections and wires. I hope you can easily find and fix the problem. Steve

  4. Hello,
    I have a problem with my HVAC. And to me it’s a weird one. My husband is deployed right now and I’m at lose of what to do. My heater hasn’t been working right in the early mornings when it’s the coldest(25-35 outride) I turn it on and it blows cold air for a bit then shuts off but the thermostat still says it’s running…then about 12 noon it will kick on and heat. I have wood stove so I only use the heat in the mornings. The heater is working fine in the evening too, just not in the morning. We have a Nest thermostat and I called them and it’s not showing errors. Was wonder what the issue is. I’m going to call and HVAC person on Monday. My unit is heat and cool about 9 years old and is gas for the heater. Thank you

    1. Hi Brandy! God bless you and your husband! Thank you both so very much for your service to our country!!! So sorry to hear that you are having trouble with your furnace getting it to heat properly. I could be wrong, but I think you might have a thermostat problem. As you said, “gas for the heater”. I am giving my suggestion based on a gas furnace set up. I would like to suggest that you turn the power off to the furnace which should turn the power off to the thermostat. Take the face off the thermostat unscrew the W (white) and R (red) wires from the thermostat. join (twist) the red and white wires together with a wire nut or electrical tape. Turn the power back on to the furnace and see if the furnace acts properly by heating your home until you turn the power off at the furnace. With the red and white wire joined together you are bypassing the thermostat so in order to turn the heat off you will need to turn the power off to the furnace. If you need more help then we have lots of furnace troubleshooting advice on the following page: I would suggest going through the troubleshooting flow chart to see what is wrong: We also have lots of troubleshooting questions and answers on the following page: If you have any specific questions please let me know. Thanks! I hope you can easily find and fix the problem. You and your husband will be in my prayers. You two are so very awesome! Thanks! Steve

  5. I have an Armstrong furnace, only about 5 years old. Interlocked to a lifebreath HRV. A couple days ago it stopped working. Everything goes right up to the igniter glowing but then no gas flows and it wouldn’t light. After a bunch of diagnostics I discovered that the problem only happens when the G terminal receives 24v commanding the fan on. If G is not activated then everything works fine, the igniter lights, gas flows, control board engages high speed on the fan and it’s all good. I discovered this because the HRV always commands the fan on when it is running so when I disconnected the interlock it started working fine. I’m able to reproduce the problem by simply turning the thermostat fan setting from Auto to On, then the thermostat sends 24v to the G terminal and during the ignition process the igniter lights but the furnace trips out when it should open the gas valve. LED indicator flashes 3 times which indicates Low-fire pressure, rollout, or aux limit switch open. From my understanding if any of those limit switches were actually open the igniter would not glow so it seems like the error code is a red herring. Any advice? Do I have a bad control board?

    1. Hi Chris! This sounds like you either have a bad control board or a bad HRV control. I do not know anything about how HRV’s are hooked up so I would suggest that you call someone who is familiar with HVR systems and how they interact with the furnace unless you know how to read how the HRV is wired. Sorry that I can not be of much help. Steve

  6. Hi, hope you can help me. I am a widow and need help with my very old electric furnace. For some reason the 2 FRN-R-60 fuses keep blowing. Can’t really afford to call someone out and can’t afford to buy fuses every week either. What could be causing this?

    1. Sorry to hear you are having trouble with your electric furnace blowing fuses. If you are using the same size fuse replacements (same amp rating) that you have always had installed then I would think that most of the time fuses blow because of loose wire connections or loose fuse connections. I would suggest that you turn off the power to your furnace and check all wire connections and fuse connections to make sure they are good and tight. Any arcing from a loose connection can cause a high amp draw and can blow fuses. I hope you can easily find and fix the problem. God bless you and your husband. I know that you will see him again someday in Heaven! Sorry for your tremendous loss! I lost my mom 3 years ago and the hope that keeps me going is knowing that I will see and be with her again!!! Always looking forward to that day! Take Care. Steve

  7. Hello, I have a Rheem Electric Furnace with Heat Pump. It is not heating the house effectively, even with Aux heat on all night. Is it possible the heating element become weakened? I have never had electric before. Thanks

    1. Hi Jeff! Yes, one of the electric heater coils could be burned out or you could have a burnt wire or a limit thermostat out. Here is a link to some good Youtube Electric furnace troubleshooting videos. I hope this will help you find and fix your problem. God bless you and your family. Steve

  8. My Lennox 80UHG Gas furnace is working properly without any heating issues. But recently I noticed that during some of the heating cycle there are few clicking sound I think coming from the direction of the gas valve. These few clicking sound happen prior to the blower kicks in and a minute or two after the blower kick in. The furnace still still work fine. Is there an issue with the gas valve if the clicking sound is from the valve?

    1. Hi! This sounds like you are losing your furnace flame sensing ability. The flame sensor briefly loses enough microamps on the flame sensor and it cuts the gas off and causes the clicking sound. It might not be enough to cut the gas valve off completely, but it almost cuts it off. I would suggest that you make sure all ground wires and connections are tight. I would suggest that you read the post on the following page and watch the videos. I hope this post will help you find and fix the problem:

  9. Good morning. We have an old Rheem 80 plus 75,000 BTU gas furnace. I believe I have a bad ignition module. The burner will light, stay on for almost one minute then shut off. This began after I replaced the inducer fan relay. Flame sensor has about 2-3 microamps-ok
    Here is what is baffling; if I add a jumper wire to the white wire(comes from the thermostat to the inducer fan relay) the flame stays lit, the burners stay on. However, the pressure switch the attached to the inducer fan will no longer shut down the burner if it opens. It is bypassed by adding the jumper. I checked all the grounds, have 24VAC at the transformer, and from what I can tell all my other connections are ok.
    Could the board have an internal short, and it is making the circuit back through the added jumper? Could the rapid opening and closing of the faulty relay have fried a circuit in the board? There are no burn or scorched solders in it.
    I’m a fairly accomplished industrial mechanic with good troubleshooting skill, but without knowing exactly how the board works I’m stuck throwing parts at it. Already put on a new pressure switch and relay. Currently it has a Honeywell S8660k ignition module.

    1. Hi Thomas! I am sorry, that I do not know what your problem could be other than possibly a control board problem. I am not familiar with how the control board works. If you would like for me to look up the control board part number then please send me your furnace model number and serial number to our email address: Sorry that I can not be of any help. Steve

  10. Hello , I have a RUUD Furnace made by RHEEM , model # R92PA1151524MSA , SERIAL # W471441154 , It was installed a month ago and everything worked fine until now , The furnace flashes code 57 meaning pressure switch open then it my flash code 58 once then sometimes code 55 once or twice witch is pressure switch closed then goes back to code 57 until it cycles off heat never coming on , if i jump pressure switch to simulate it closing the furnace cycle on and heat comes on then blower ,,,all works . once the heat is not called for furnace turns off . if i leave the jumper wire in it will not come back on unless i break the connection then make it . I replaced the pressure switch a new one and it does the same thing . it seems that there is not enough negative pressure to pill in the pressure switch , HELP ! any suggestions would be great

    1. Hi Patrick! We have a post about pressure switch problems on the following page: I hope this helps you find and fix the problem. If you have any questions please email at Hope you have a great Thanksgiving! Steve

  11. Hi Steve,
    Wow lots of great info on your site! Thanks for sharing!!
    My electric furnace is “releasing pressure” with a loud hissing sound every 7-8 minutes. Is there a common cause for this? The unit was new in 2016.

    1. Hi Cindy! Most hissing sounds are caused by either refrigerant flowing through the refrigerant lines inside your air handler if you have a heat pump or a loose electrical connection that is arcing. Both causes should be looked into by an HVAC tech and fixed. Your unit should not be making this hissing sound every 7 to 8 minutes. Please let me know when you find out what the problem is so we can post it for others to see in case they have this problem. I hope you can easily find and fix the problem. Steve

  12. Is this normal? My utility company says “yes.” But, I still wonder. My forced air electric furnace is in a crawl space under my northen snow-region ranch-style home. I know from being in that crawl space that the vents in the foundation do cause that area to get chilly. The set temperature on my fairly new thermostat is 54 degrees F. The room temperature is about 63 F. While the set temperature to trigger the fan to turn on has not been reached, I noticed my cat was laying atop one vent — the vent directly above the rectangular furnace attached to the wall in the crawl space. All of the other vents in the house are as they should be, cool. The fan is not blowing. There is just a gentle feeling of heat coming from that vent.

    Is that normal??

    1. Hi Cindy! I really do not understand what is going on for sure with your electric furnace. If the set temperature on your thermostat is set to 54 degrees and the room temperature is 63 degrees. Then nothing should be running. No heat should be coming out of the registers and your electric furnace should be off. If you are getting some heat out of the registers with the thermostat set to 54 then this is not normal. You might have a stuck sequencer that is keeping one or more of the electric heaters on and this will run your electric bill way up. With your thermostat set to 54, I would suggest that you go to your electric meter and see if it is spinning slow or fast. If it is spinning fast then this is a good sign that your electric heaters are ON and something (a relay or sequencer) is stuck ON. If you turn your thermostat above 63 your electric furnace’s electric heaters should come on and shortly after that (10 to 30 seconds) the blower should come on and blow warm air. I hope you can find the problem because if an electric heater is stuck on you will have a super high electric bill. God Bless you and your family. Steve

      1. Thanks and yikes. I’m glad I asked as the utility company’s respose was “There will always be a little energy coming our of your electric furnace, particularly if it’s in a cold crawl space, and the only way to turn it off completely is to turn it off at the meter. ” My intuition said that this seemed odd. My heat bill has increased by 200-300 kWh.

        There is no heat coming out of any register anywhere in the house except for the single one that sits directly above the furnace itself. The heat coming out is tiny. I can lay my hand on the register and not feel a need to remove it. And the house temperature has not risen above 62. I am going to throw the breakers on everything except the furnace and see what that does to the meter. I turned the programmable thermostat off and I still felt the little bit of heat whisping through the single vent. Will then check the electric meter. My check with everything on (freezer, refrigerator, desktop computer, ) showed it moving but it didn’t seem fast to my untrained eye. I’m a widow and now in learn mode after being spoiled for 45 years by a wonderful handy husband. Living alone out in the middle of nowhere makes all of this more challenging. I greatly appreciate your kind and quick response. You are helping someone!!! And for that, I’m grateful.

      2. Hi Cindy! Thank you so very much for your kind words! If the furnace has not run for a while, then I do not see why any heat at all should be coming out of even one register. I hope you can find and fix the problem if there is a problem at all. If there is a problem with one of the heaters staying on then I do not want you to have a sky-high electric bill. God bless you and your husband. Sounds like your husband was a great and awesome man! Sorry for your loss, but I know that you will see him again in heaven! Amen. Steve

      3. While the electric meter does not seem to be running away fast, I went ahead and turned off the furnace breaker, which I saw was in a box separate from the other breakers. (As I said, I’m in “learn how to do everything in the house repair” mode.) Going now to google sequencers. I wonder if it’s something I can learn to fix. Huge bill from anyone just to drive to my place — before any work is done or even for a consult. Soo, I always want to know if I can learn it first. Thank you so much for giving of you! Blessings!!

      4. Thank you so very much for your kind words and blessings.

  13. Hi Steve,
    I cant believe all the useful information I found on your website, Thank You. I am experiencing a strange problem that I cant seem to understand. My York single stage heater (installed last year) is not igniting. The heat cycle starts with the fan turning on, igniter glowing red hot, gas valve opens and I hear the gas come out. BUT no ignition! Ive already replaced the gas valve and that did not solve my problem. I’ve noticed that when I blow into the burner tube next to the igniter, it ignites every time. I already had the gas company come out and replace my meter and regulator with no luck. My other gas appliances have no issues. What do you think?

    1. Hi Dan! This sounds like you need to have the gas valve pressure adjusted properly. On LP gas, especially and with natural gas, the air/gas mixture is critical to have proper ignition. I would suggest getting a tech who knows how to adjust gas pressure properly with a manometer to get your gas pressure adjusted correctly. There is an adjustment screw on the gas valve. Here is a link to a good video on how to adjust gas pressure: Also, proper placement of the ignitor is critical. The ignitor should be located close to the burner where the gas comes out. I hope you can easily and inexpensively get this problem fixed. Steve

  14. Hi Steve,
    Thank you for hosting this great forum. My Honeywell furnace is kicking on for short periods and shutting off before reaching the temp set on the thermostat. I get the soft lockout main limit open too long error code. This has happened before and the filter I had wasn’t really dirty but it was a little flimsy and bent in a little bit so I thought that was tripping something. It worked fine after I changed the filter. That was about a month ago and now it’s doing the same thing with a different filter. It does have some dirt on it but doesn’t seem like it would be restrictive but I’m assuming even though the filter I have now isn’t bent in that it is still tripping the system because of the dirt on it. Do you recommend a certain type/brand of filter? Thank you again!

    1. Hi Geoff! Thank you so very much for your question and kind words! I would recommend a filter that is merv 8 or less. The higher merv rated filters sometimes restrict the air flow too much. Here is a pretty good video that shows about troubleshooting a limit switch: Here is another good Youtube video on limit switches: I would suggest that once you find the limit to test the limit and make sure it is staying closed when the gas cuts off. If the limit is shutting the gas off on your furnace then this is a sure sign that the furnace is over-heating. Over-heating can be caused by a dirty blower wheel, dirty evaporator coil (stopped up) slow blower motor, (might need to move to a higher speed or need a new run capacitor) duct work that is too small or a gas valve that is adjust too high allowing too much input BTU’s to be burnt in the heat exchanger. Of course a dirty filter could also cause the furnace to over heat. I hope you can easily find and fix the problem. Steve

      1. Wow, amazing response time, Steve! Thank you very much. I’ll follow the videos and I’m going to run out and get a new filter today. Hopefully this will put an end to it:-)

  15. My electric furnace will work in the van on position but not auto. What could be the cause

    1. More than likely you have a thermostat problem. On most electric furnace thermostats the fan is energized when the thermostat calls for heat. Sometimes the fan is energized through a timed sequencer. I would think that you either have a thermostat problem or a sequencer problem. You would need to troubleshoot with a volt meter. I hope you can easily find and fix the problem. Steve

  16. I have a Bryant gas furnace that I have to go and manually press and release the door switch for the furnace to kick on? Could it be something as simple as replacing the Bryant Furnace Door Switch HR54ZA006 or is it something more sinister? Thanks Chad

    1. Hi Chad! It could be something as simple as the furnace door switch. You should be able to wire around the switch temporarily to see it that fixes the problem. If the furnace is lighting properly and running properly after resetting the door switch then I would say that it is the door switch. I hope it is as easy a fix as the door switch. Steve

  17. Good morning, I have an electric furnace that requires a breaker off reset and fiddling with the mild/warm weather switch. This is the only way we have been able to get the heat to come back on again. At first this fix would last a week or two but now its only a few hours. We think the switch needs replacing but aren’t sure. I have gone through the list of possibilities from dirty filter to condensation and nothing fits. The only thing that works is fiddling with the switch. It is currently -40 c outside and I woke up to no heat….

    1. Hi Michelle! I am so sorry that your electric furnace is not working properly. Most of the time the cause for multiple breaker resets is that the breaker is bad or there is a loose connection inside the electric heater compartment. I would suggest checking to see if the outside of your breaker is warm before it trips. Sometimes I have heard the breakers arcing inside. If the breaker is warm on the outside then this is a sure sign that the breaker is going out. Here is a link to a good video on troubleshooting sequencers and electric furnaces. This sounds like a breaker problem to me. I hope you can get it fixed soon! Steve

  18. Hi Steve,
    I have a Nordyne M1MB077AAW forced air natural gas furnace. I think it is abort 10 years old, 80%. When the thermostat clicks on the exhaust fan motor turns on and then the igniter glows red (I replaced it last year) but then the gas valve does not open and I hear a couple clicks and everything shuts off. Checked the pressure switch. No codes from leds on board, just solid red led until everything shuts off. Checked voltage at gas valve with leads attached, nothing until right before it shuts off, but only a couple volts. Led also turns off when it shuts off. Second most ordered item at repair clinic is control board. Thanks in advance for any advice.

    1. Hi! Sorry you are having trouble with your furnace. If all the safety controls (limit, rollouts pressure switch) are closed and the gas valve is not getting any voltage, then this sounds like a control board problem to me. So, you probably need a new control board. Please make sure all your connections are tight and your ground screw is tight. I am sorry, I do not have a Nordyne parts program where I can look up parts. I hope you can get your furnace fixed soon. Steve

      1. Thanks for quick response. Checked all connections and grounds. Everything looks good. Found new board from good Amazon seller for $77, so not too bad. I’m in Southern Calif so not too urgent. Thanks again. Happy Holidays. Mike

  19. Hello, thank you so much for sharing your knowledge. I am in hopes you can point me in the right direction. I have an American Standard Freedom 80 installed in 2000. It was blowing cool air for a couple minutes, then lukewarm air for 5-10 minutes and the cold air for a couple minutes. The cold air would drop the temp in the house so it would repeat the cycle every 2-5 minutes. It had an washable electrostatic filter and sounded like it was working really hard even though I cleaned the filter before winter arrived. I put a very cheap filter in today and that helped some. Cold cycle at beginning and end is much shorter and temp stays up for 15 minutes instead of 2-5 so running probably a third as much. But it is still only blowing Lukewarm air instead of hot air. I have a fireplace and burned wood a good bit today and the house stayed comfortable so I don’t think the chilly air coming from upstairs is a heat loss issue as much as it is the cold/cool air the furnace is blowing into the house. House is on a slab with ductwork underground. Is there anything you could suggest I try? Thank you so much.

    1. Hi Laura! Sorry that your furnace is not heating your home well. I would guess that gas burners on your furnace are shutting off and on and not staying on long enough to heat your home. If the burners are cutting off and on for short periods of burn time then you will need to find out what it cutting the burners off prematurely. I would suggest that you purchase a cheap volt meter at Home Depot or your local hardware store so you can do some testing. There are several things that can cause the burners to go off prematurely. A thermostat where the batteries are low or if the thermostat is going bad can cause the furnace to cycle off and on. I would suggest that you test with a volt meter between W and C (com) on your control board to see if the thermostat is supplying a constant 24 to 28 volts to the control board to keep the furnace burning. If you lose voltage between W and C then your thermostat is the problem. Another problem would be if the furnace is over-heating your limit might be turning the furnace off and on. You say that the furnace improved when you changed filters so maybe you have something that is causing the limit to go off and shut the furnace off and ON. We have a post and video about limits and rollouts switches on the following page: If your limit is shutting your furnace off and ON then this could be caused by a dirty filter, blower wheel evaporator coil, a restriction in the return or supply duct line, or a faulty limit switch. I would suggest going through the troubleshooting flow chart to see what is wrong: We also have lots of troubleshooting questions and answers on the following page: If you have any specific questions please let me know. If you would like for me to look up parts please email me your furnace’s model number and I will be glad to look parts up for you. Our email address is: Thanks! I hope you can easily find and fix the problem.

      1. Hi Steve,

        Thank you so much for your reply and all of the information you provided. I took the front panels off today and turned the thermostat up to 75. The furnace seems to be operating properly – flame does not go out, it stays on until the thermostat reaches the temp it is set to (it also did when set at 71). When set at 71 the heat it blows is never more than lukewarm. Set at 75 it felt warmer but not hot. I sealed an area in the duct above the filter that was pulling air but this didn’t seem to change anything. Changing the filter yesterday helped the cool down time so it wasn’t blowing as much cold air in the house. This was dropping the temp in the house making the furnace run more frequently. So essentially it is a question of why it only blows Luke warm air (please forgive my very limited knowledge on how this works). Volt meter tests are likely beyond what I am comfortable messing with. Could it be that the underground ductwork is just cooling off the air before it reaches the interior of the house (it’s pretty cold here)? Could a dirty igniter or flame sensor be an issue if it stays lit until the thermostat reaches the set temp?

      2. Hi! No, since the furnace is running a dirty igniter or flame sensor is not the problem. The furnace would not run if the flame sensor or ignitor were bad. If the flame sensor is bad the furnace igniter would light the burners for 8 to 10 seconds then cut the burners off. Your cold underground duct work could be causing some of the problem, but most of the time under ground things stay at one temperature unless it is super cold below zero outside. You might not have a big enough furnace and blower since the furnace is only blowing luke warm air. I would suggest that if you have any return duct work in the attic or in any unconditioned space that you make sure it is sealed up and not drawing in cold air. Sorry that I can not be much help. If the furnace worked well in the past then a new furnace is not the solution. You might have a tech increase the gas input on the gas valve and turn up the blower speed if possible on your existing furnace to get more BTU’s out of it. I hope you can find out the problem. Please let me know if you find out a solution. God bless you. Steve

  20. Mr. and Mrs. Arnold,
    Maybe you can help me. I have an International Products Co furnace , Mod No. END4X3OL17A1. The problem I have is intermittent and the people who installed it haven’t been able to figure out anything. The furnace starts and blows heat for 3 minutes, goes off and gives Code 4 signal. In a few minutes this changes to Code 7. In 3 hrs. the unit starts and may run properly or, too often, shuts down after 3 minutes, with the same Code 4 and Code 7 indications. The unit may work fine for most of a day, then start the shut off, wait 3 hrs., routine again. On one day this week it happened 4 times taking 12 hours of the day with no heat. The next day I set the thermostat when I got up, and the unit worked fine all day. Some days the shut down routine occurs once, sometimes twice. Only once did it fail to run right 4 times. The problem occurs nearly every day though. Maybe my guys aren’t experienced enough or something but they haven’t come up with anything. By the way, the furnace is only 2 years old.
    Thank you very much for any advice or other help you may be able to give me.

    1. Hi Neal! So sorry to hear that you have had all this trouble with your furnace and it is only 2 years old. You should have a warranty I hope to pay for the repairs. I would like to suggest that you look on the furnace door and see what the code 4 and Code 7 means. I am not familiar with your furnace. Most of the time the new furnaces are built to tell the repair person what the problem is by reading the flash codes. This is one of those problems where you are going to have to test and see where the problem is the next time the problem occurs. I would start with making sure the thermostat is supplying a constant 24 to 28 volts between the W and C (com) terminals. If the thermostat is cutting off between W and C then the thermostat is the problem. I would suggest making sure all the wires and connections are good and tight. If this is a condensing furnace with plastic pipe then I would look to see if the installers followed the manufacturer’s guide lines on the amount or pipe and turns there can be accepted in the furnace venting. Too many turns and too much pipe can cause lock out problems like you are having. I could not look up the parts for your furnace because the model number you sent is for the cased AC coil. The furnace model number should be inside the furnace near the burners. So other things that might help are the following: We have lots of furnace troubleshooting advice on the following page: I would suggest going through the troubleshooting flow chart to see what is wrong: We also have lots of troubleshooting questions and answers on the following page: If you have any specific questions please let me know. Thanks! I hope you can easily find and fix the problem.

  21. Hi there,
    I have Trane XB Gas furnace. After 5-6 min it stops works. If I take burners cover off it works fine, but soon I putt it back it stopped working.

    1. Hi Lenny! This sounds like you might have a stopped up vent pipe or a leak in the vent system. I say this because you say that the furnace runs fine when the burner cover is off. I would make sure that your vent system both intake and exhaust are not obstructed. If this is a condensing furnace that produces water when heating then you might want to make sure your drain system is not partially stopped up. I would suggest taking the pressure switch tube off so the pressure switch does not get damaged and sucking the drain for the furnace out with a wet vac. Also make sure the draft inducer is working at full speed. If the inducer has a capacitor I would recommend making sure the capacitor is in good shape so you know the inducer is working right. I hope you can easily find and fix the problem. Steve

  22. Sir,
    We have euro 10g combastion furnace for pasteurizer.if I put the burner outside it’s working ones I put back inside of pasteurizer it will off. any suggestions will help us…thx

    1. Hi Ramon! Sorry, I do not know much of anything about pasteurizers, but since the burner works outside and not inside the pasteurizer I would think that the burner is not getting enough combustion air or the vent is stopped up. I would suggest making sure the exhaust vent is open. You might have to turn the gas pressure down some so the gas valve so the gas has enough air to burn. If the burn requires too much air it will go out. I am sorry that I can not be of much help. I hope you can easily find and fix the problem. Steve

  23. Hi I have a Goodman gmp125-5. I am having problems with the ignitor glowing. I have replaced and tested my new ignitor and everything seems good. I also tested the voltage coming into the ignitor and it starts to give me voltage but then stops. I’m thinking I have a bad control board. I get one flash on the light when the furnace fails. I can also light the furnace with a long match and it works fine until I turn it off. Thanks for your advice.

    1. Hi Mr. Lamont! This does sound like a relay on the control board is bad and not sending the 110 volts to light your ignitor. I would say check all your rollouts and limit to make sure they are closed until you said that the ignitor starts to have voltage and then the voltage drops out. Our Goodman parts program shows that your furnace uses control board part number B1809913S like we sell on the following page: The ignitor your furnace uses is a B1401018S like we sell on the following page: I hope you can get your furnace fixed soon. Steve

  24. Hello,

    I’d greatly appreciate your help. I have a Bryan Plus 90 350MAV. The blower motor will not start. I originally thought it was just a bad motor so I bought a new one. It turns out the resistance measurements on the old and new motor are about the same. So, it’s likely not the motor. I’ve also measured the capacitor and it checks out, too. Lastly, the 5 amp fuse seems to be perfectly fine. This is the real confusing part: I’ve disconnected the motor and started the heat – the burner starts, runs for a few seconds, and then I hear the relay click and measure the proper ~115V to the motor. So far so good. I hook the new motor up and start the heat – the burner starts, runs for a few seconds, and then I hear the relay click but no voltage. I measure 0V when the new motor is connected and 115V when it is just an open circuit. Again, the resistance measurements are OK. Do you know what could possibly cause this? I’m leaning toward it having to do with the control board.

    1. Hi Matt! More than likely you have a bad relay on the control board. When a load like the motor is applied to the circuit the relay can not supply the voltage so the motor does not start. I would suggest a new control board. I will need you full Bryant furnace product number in order to recommend the correct control board. I hope you have a nice day! Steve

  25. Mr. Arnold

    I have a Coleman electric furnace, when the thermostat calls for heat the furnace elements heat up but the blower motor is delayed in starting. When it does start the motor makes a banging noise any suggestions?

    1. Hi Jerry! I would suggest turning the power off to the air handlers and to use a mirror with flash light to see if you can see any foreign object inside the blower wheel. I would make sure the blower wheel is tight on the blower motor shaft and make sure the blower wheel is free to spin. You should be able to spin the blower wheel by hand and it should continue to turn for a few seconds after you spin it. Sometimes the blower wheel fins can become loose and cause and awful racket. The fins can come loose from the inner part of the blower wheel which holds them in place. If you feel looseness in the fins of the wheel then you will need a new blower wheel. I would also suggest that you check the capacitor to make sure the blower motor capacitor is in good shape. A weak capacitor can cause a blower motor to not sound right (lots of humming and make the blower slow). I hope you can easily find and fix the problem. Steve

  26. Mr. Arnold,
    I am having trouble figuring out why I am getting 57v at the limit switch, which gives the relays the 24v on my electric coils. Which is causing my relays to not close and turn on the electric coils. I have a 2-stage Aircoaire heat strip model AMFK10. I am freezing right now with no heat and I am confused why I am getting 24v from the transformer to the board but through the board I get the 57v. I have tried getting 24v from elsewhere but fails to trigger the relays. I can push the override on the relay and the elements turn red. Please help me out if you have the time. I thank you in advance for your help.

    1. Hi Daniel! Sorry to hear that your electric heat is not working. This sounds like a short to somewhere in your system. This could be in your control board or in another control like a sequencer or relay. I would suggest trying to trace the 24 volts from the thermostat. This should be the white “W” wire to common inside your air handler. Try to test the wires through the air handler and were the voltage turns to 57 volts then this is where the problem is. If the low voltage is going into the control board 24 volts and coming out of the control board at 57 volts then I would think you have a bad control board. I looked up the parts for your 10 KW heater and they show part numbers: 1084734 limit switch, part number: 1172506 relay, a terminal block 1087753 and a fuse terminal 1087811. That is about all the parts they show. Sorry that I can not give you a better answer. This is the way that I would try to troubleshoot this problem. I hope you can easily find and fix the problem. Steve

  27. I have an issue with an older Carrier furnace, when the burner box has the sight glass in place the tube on the far right side ( the ignition side ) goes out for a second or two and then relights with a small popping sound and after a few minutes will shut the burners back off. After 3 times it will lock out and need reset. With the glass out the furnace will continue to run normally. The technician feels that this is indicative of a bad heat ex-changer which costs about 700.00 for the part alone. Is it possible that this is being caused by dirt or debris in that one tube cutting the gas flow intermittently? I can replace the entire furnace for a couple hundred more than the heat ex-changer so it doesnt seem prudent to replace it on an older furnace that was updated in 2007. It is an 80,000 BTU 90% efficiency furnace. If it is possibly a smaller issue isolated to the burner tube it would be worth the time to disassemble and visually inspect the burner assembly. The flame sensor has been replaced as we originally thought this was the problem. All the rest of the tubes including the one with the flame sensor stay lit reliably.

    1. Hi Mr. Young! I would suggest that you take the burners out and clean them, blow them out with compressed air. I have also seen this happen when there is a leak in the combustion system like a leak in the burner box or heat ex-changer. I would sure try to clean the burner tubes and make sure the condensate drain is draining properly. I would suggest taking the pressure switch tube off that goes to the pressure switch so it does not damage the pressure switch, then take a wet vac to the condensate drain lines to make sure the condensate line and the secondary heat ex-changer drain are not stopped up. Yes, with the flames not going all the way across to the flame sensor, the flame sensor can not sense the flame and the burners go out. If you can get it to burn all the way across to the flame sensor side then your problems should be solved. I hope that cleaning the burners and condensate drain fixes your problem. Steve

  28. Dear Mr Arnold,

    I have a 80,000 output btu Goodman furnace, (GMP 100-5) which is about 30 yrs old. last month it devoloped a vibration at the burner box, it starts up after about 3 to 4 mins and is continuous when heating . I have tighted all the screws but vibration persits, starts up fine with all flames on.
    When I push againist the box where the burners are srewed in like a object such as a screw drive or piece of wood it stops, but when pulled away the vibration starts again. I Have spun the squirrel cage and it seems fine, no rubbing or stopping and no looseness felt. The vibration is only at the box where the Flame outputs are.
    Any ideas ?


    1. Hi Paul! I have seen this vibration problem before similar to yours. I remember I had to get the burners positioned just in the right place and then tighten all the screws especially around the screws that hold the gas manifold and burners in place. This took me some trail and errors to get it to stop rattling. I have also seen other furnaces where one or more of the metal baffles that direct air flow up inside the heat exchanger become loose and start to rattle. Several times I would have to pull the whole blower assembly out and look up inside the heat exchanger with a flash light to see if any of the baffles, air diverters were loose. Several times I found loose baffles and had to tighten them up before the rattling noise stopped. I hope you can easily find and fix this noisy problem without having to pull the blower assembly! Steve

  29. Hello Steve,

    I have a Carrier furnace, Model N8MSL0451412A1 that is giving an error of three blinking lights (pressure switch did not close). I started out by replacing that switch, did not help. I then had someone come out to take a look at it, they said I had a bad inducer motor and that the part would be $400 and another $400 to install it. I got the part myself for $120 and installed it in about 30 minutes but that didn’t fix the problem either.

    In getting into it I discovered that there was no filter inline, I added a filter at the return air in the floor of the house. I opened up both sides of the furnace to make sure there weren’t any obstructions (pretty dirty as you could imagine, I cleaned all the gunk out), as well as disconnecting the exhaust side to see if it would run ok with only a short section of exhaust (to make sure it wasn’t obstructed further upstream). Still nothing.

    After that I found your website, I wish I’d found it sooner! I started checking voltages as your troubleshooting suggests and found:

    At the furnace terminals:
    W to C, R to C, G to W, and G to R are all giving just under 28 volts.

    If I take the thermostat plate off inside the house I get:
    W to R and G to R just under 28v. G to W, C to W, C to R all giving 0v.

    All rollout switches are giving 28v from both sides to ground.

    The pressure switch is giving 28v from the positive side (yellow) to ground, the negative side (orange) is giving 0v to ground.

    I run the diagnostic test on it and the igniter glows so seems like that is fine. I did recently change out the thermostat, the old one face display wasn’t working. I really don’t know if the furnace was working at that point, it wasn’t cold enough to need it but every few days at that time. Unfortunately my kids got a hold of that thermostat when I took it off rendering it unusable to try if I could put it back on and make it work.

    Does it seem like I have a bad control board? That’s about the only thing left to replace as far as I can tell. Thanks in advance to any advice you can give, I’m running out of firewood and need to get this thing back running!!


    1. Hi Andy!
      Sorry to hear that you are having trouble with your furnace. I was wanting to look at the parts your furnace has, but our Carrier parts program does not find any furnaces that start with “N8MSL” Please recheck your furnace model number. Please check your limit on each side to ground and make sure it is giving 24 volts on each side. This probably is not the problem, but your furnace air flow might be partially stopped up since you did not have a filter installed. If you have air conditioning the evaporator coil could very well be stopped up with lint and dirt which creates an air restriction and might cause the furnace to go out on limit. From your troubleshooting you say that with the draft inducer running you are not getting 24 volts to both terminals to ground? This is a sure sign you have a pressure switch, draft inducer or stopped up vent. If you have an 80% furnace it will not have a condensate drain on the furnace. Only high efficiency 92% furnaces with secondary heat exchangers produce water in the winter and have condensate drains. I would suggest making sure the hole which the pressure switch attaches to on the draft inducer is not stopped up. I would suggest running a small drill bit in the hole just to make sure the hole is open. Please make sure that the new draft inducer that you installed is sealed with a gasket to the body of the furnace. Any air leaks will cause the pressure switch to not close. It is normal to have between 24 and 28 volts when you test the components. You could need a control board, but this sounds like a pressure switch problem or a draft inducer problem. It would be best to correspond further from my email address if you want me to look up parts or ask any other questions I will be glad to try and help. I hope you can find and fix the problem. Steve

  30. Amana model AMS90704CXA no problems on 10 year old machine, 1 month ago had service for no heat, replaced inducer motor, now fills up with water very quickly, no drain on bottom of fan or any way for water to get out. Seems to be coming in from exhaust pipe that exits inducer fan from top left out and up to crawlspace ceiling and outside. Should there be a drain on bottom inducer fan? I can take it off and empty and runs fine. Or should there be a trap on exhaust line? Exhaust pipe has a slant slightly down toward the furnace

    1. Hi Jim! Sounds like the condensate drain on your furnace is not hooked up properly. I will send you a pdf parts list that I copied from our Amana parts program in the email that you have on this post. I will send it to the yahoo email address. This pdf shows some parts for the drain on your furnace. I hope this helps you solve your problem. Steve

  31. I have a bryant natural gas model 373LAV036070. Blower on unit just periodically works. Sometimes it will work for a day and then other times it may only work for about 15 seconds and shuts back off. This occurs even when furnace is lit which leads to it overheating and tripping flame roll out sensor. All that gas to be done to get the blower to run again is turning breaker off and back on which leads me to think it isn’t the motor going bad. I have checked ducts for obstructions, cleaned motor and blower/entire furnace, put in new start capacitor all to no avail.

    1. Hi Clay! This sounds like you either have a weak blower motor capacitor (the least expensive fix) or a bad control board or blower motor. I would suggest the you get the motor run capacitor checked out to make sure it is good. If a new capacitor does not fix the problem then I would recommend the next time the blower motor will not start to tape the furnace blower door safety switch closed so you can test the control board with a volt meter. Set your volt meter to “Volts Ac” Please test the lead that controls the Heat speed which goes to the blower motor (usually marked heat on the control board) touch the other lead to neutral. You should be getting 110 to 120 volts AC to the blower motor coming out of the control board. If you aren’t then you have a bad relay on the control board and you need a new board. If you are getting 110 volts out and the motor is not running then you need a new blower motor. Another test would be to set the thermostat to “Fan ON” and see if the blower will work. If the blower works OK with “Fan ON” then more than likely it is a problem with the control board. Please send me you furnace’s product number if you would like for me to recommend parts. There should be 4 letters at the end of the model number that you provided. Please email me at: with the product number. I hope you can find and fix the problem. Steve

  32. I’ve got a Payne giving me a code 31. I removed and cleaned out the condensation box (full of crud) and no water came out of the large tube going to the inducer motor, I figured no water in the inducer. Unit still will not fire up. So I checked the 1/4″ tube running from the pressure switch to the hard-to-reach area in back of the inducer motor and I can neither blow into it nor suck out of it. Now on an identical unit, I was able to suck the tube clear (thankfully no crud in mouth) and that thing fired right up. So I figure this clogged tube is the problem again. But I can’t suck (or blow) in it. It’s really clogged. So my question is this: use a bike pump, ball inflator and some duct tape to BLOW the clog into the inducer, or use a vacuum cleaner, more duct tape and a small funnel that fits into the 1/4″ tube to SUCK the clog out. Thoughts? Better ideas? I’m a newbie and do not want to take that inducer motor off! Thanks!

    1. Hi Charles! I would suggest trying to run some warm water into the top of the inducer if the inducer has a tube near the top where you can squirt some water in. Many of the Bryant, Carrier furnaces want you to prime them with water before using them the first time. I would make sure that any pressure switch hoses are disconnected, because using a vac or your mouth to suck on the system could cause the pressure switch to be destroyed. If you have an air compressor or like you say a bike pump to blow the line out would be good. If you use an air compressor please make sure you have an opening in the draft inducer to let the air escape. Most of the time I use a wet vac and pour water from the top and suck the water out the bottom. Man! that must be a bad clog! Best of luck in getting the furnace unclogged and fixed. Steve

  33. Steve, I have a Goodman GMP-050-3 Natural gas split system with AC upstairs. I woke up one morning a few months ago and the house downstairs was 62 degrees, I went upstairs and the thermostat was blank(digital)and it seemed to be “stuck” in cooling mode. I shut the power off to the unit and when I brought the unit back up the digital thermostat was still blank and the unit will not turn on in heating or cooling mode, the unit is about 16 years old?,,, any help or advice would be greatly appreciated.

    PS, I did do some internet researching and they said the possible cause was a bad control board, this has been replaced, and still the same problem exists.

    1. Hi Bill! Sorry to hear that you furnace is not working! We need heat these days! Since you say that your thermostat is blank. I would look to what is not powering your thermostat such as a blown fuse on the control board, low thermostat batteries (if equipped). A transformer that is not producing 24 to 28 voltage on the low voltage side. If you have a thermostat with a C (com) connection you should be getting 24 to 28 volts AC between the R and C terminals on the thermostat. If you aren’t then you have a low voltage power problem. Please make sure the high voltage is turned on (switch on the side) the furnace. When I was doing service work this is one of the first questions we would ask customers to check before I made a service call, “Is the switch on the side of the furnace turned on? Is the breaker to the furnace turned on?” You would be surprised how many times that all the problem was a turned off switch or breaker. I hope the solution to your problem is that simple. If you need parts please email me at: and I will give you a parts list. Steve

  34. Hello Mr and ms Arnold! I stumbled upon your website while doing some research, i have a heil 5000 model # NUG5075BFA2. i replaced the honeywell gas valve due to a noise it was making, i have a raised ranch house, living space second floor garage with furnace on 1st floor, the noise i am getting is when the gas valve initially turns on for the pilot light there is a loud click that can be heard on second floor that seems to echo through out the hvac system, after the burners turn on there is another audible knock/click noise noted, after the burners and the gas valve shut off there is another knock/click, so like i said i replaced the gas valve and the new valve is making the same noise, i did use a manometer to make sure the manifold pressure is 3.5 inches of column water and my inlet pressure is 6 inches of column water, i lowered the manifold pressure for grins to 3 and it still has the same noise, would you have any ideas as to what could be causing this noise? any advise would be greatly appreciated

    1. Hi Chevyguy28! There are only a few things that I can think of that may cause the noise your describe. Noise can be caused when the gas valve is not getting enough low voltage. If the gas valve isn’t getting 24 to 28 volts AC then the gas valve solenoid will sometimes shutter and vibrate because it is not getting enough voltage. I have seen this happen in contactors so I believe that it could happen in gas valves too. If this is the problem then you might have another control that is robbing the voltage or you might have a weak low voltage transformer. The other noise related things that I can think of would be the heat exchanger or duct work popping or cracking as the furnace heats and cools down. Another problem that could cause noise would be delayed ignition of the gas. Please watch the gas as it lights. The gas burners should light evenly without delayed ignition. Delayed ignition would cause a mini explosion and can most definitely cause noise. I would suggest making sure all the burners, gas orifices and pilot are clean. You might think about blowing the burners and gas orifices out with compressed air. Dirty burners and partially stopped up gas orifices can cause funny noises. I hope you can easily find and fix the problem. Steve Arnold

  35. Hi, I have a fairly old York P3UR gas furnace with what I think is an odd problem. The furnace runs and will heat the house, however sometimes when it runs it emits a very strong, constant, low-pitched vibration that you can hear/feel throughout the house. It sounds EXACTLY like a semi is idling just outside the house. I do not believe it has anything to do with the duct air fan, as it occurs before the air fan comes on. It occurs with a fresh duct air filter. It is a constant, steady vibration that only stops when the burners go out. I can see what appears to be healthy flame in the burner box window. When the rumble occurs, if I move my open hand around the burner box, there are a couple places where I can feel vibrating pulses of air coming out of the burner box, which seem to be the same frequency as the vibration. It feels like the air in the burner box is oscillating and/or pulsing very rapidly for some reason. Any idea what might be causing this? Thanks for any advice.

    1. Hi! This sounds like it could possibly be a restriction in the gas orifices or too much or too light gas pressure. You might try blowing out the burners and gas orifices with compressed air. If this does not eliminate the noise the try adjusting the gas pressure down a little bit, no more than 1/4 turn at a time. After adjusting the gas pressure make sure the furnace lights properly when the furnace is cold without delayed ignition. Have you finger on the on/off switch if you see the furnace is going to have delayed ignition so you can turn the furnace off right away and you do not get a gas build up and a mini-explosion. I found this information when I googled how to adjust a gas valve: Please be careful when working with natural gas. I hope this is the problem. I have heard this happen before which sounds like the problem. I hope you get it fixed soon. Thanks so much for asking this question. Steve

  36. Bryant furnace.. When the upper cover is off the furnace lights n burns good, when i put cover back on furnace goes our… I made sure water was draining , tool off vac lines it is clicking when i suck on them n ran a sewer ogger through intake pipe ???

    1. Hi Mr. Carli! Sorry to hear you are having problems with your furnace. This sounds like you might be having a pressure switch problem due to a possible restriction in the vent lines, drain lines, draft inducer or secondary heat exchanger (if equipped). This could also be caused by a draft inducer that is running too slow. If the draft inducer has a capacitor you might want to check the capacitor to make sure it is up to specs. I am guessing that when you take the burner door off the burner compartment, if this is a seal combustion furnace the burners light and burn, but when you install the door the furnace will not burn. Please test the pressure switch to see it if is closing when the furnace will not work. If the pressure switch will not close then you might have a bad pressure switch, a blocked vent or condensate drain system, secondary heat exchanger blockage etc. It sounds like you have already tried to correct the vent and drain blockage part. Please make sure you disconnect the pressure switch when using a vac and do not suck on the pressure switch with your mouth because I heard this can damage the pressure switch. Please send me your furnace product number if you want me to look up parts. I really do not know for sure what you are dealing with without seeing the furnace. Sorry that I can not be of much help. Best of luck in finding and fixing the problem. Steve

    2. I’ve got the same problem with a Bryant 90i high efficiency furnace. Fuel is propane. The furnace is supplied and exhausted from the outside through a combination pipe. The ignition sequence proceeds properly: the igniter lights up, the gas valve is energized, but the gas does not ignite. I have been told the gas valve can stick, so when I hear it click I tap on the valve body. Sometimes this works. However, last night I removed the sight glass from the combustion box and since then the furnace has started with no problems. I can feel a suction through the sight glass hole when everything is running. Last time I checked the inducer pull I had 3.5″ WC on low heat, and 5.5″ WC on high heat (measured between inducer and pressure switches). I have also removed and cleaned out the condensate trap, as I found out it can get plugged with mold. I have a new gas valve on order, but I am suspecting that may not be the problem. Any suggestions?

      1. Hi! Since you removed the sight glass and the furnace has been working fine…this is a sign that the vent is stopped up, is too long (too many turns), or the draft inducer is dirty or too slow to produce enough air. Please make sure both your intake and supply vent piping are not obstructed if this is possible. I have a Bryant 90i furnace and if I remove the sight glass or have an air leak in the combustion chamber like from around the ignitor the pressure switch will not close and the furnace will not allow the gas valve to open. This sounds like you have a vent problem either in the vent pipes or draft inducer. Propane gas can be very difficult to adjust properly to get the right air fuel mixture. You might want to call in a professional to look at this. I hope you can easily find and fix the problem. Steve

      2. Steve, thanks for the quick response. I wound up taking apart the vent pipes and running a drain snake through each one. Unfortunately, I did not find any blockage that would have been the smoking gun. The pipes seemed clean. And the burner would still not light reliably with the sight glass installed.
        A little more to the puzzle: about a week before, the furnace quit working. I went through the possible problems until it became apparent that we had run out of propane. I checked the tank and that was the case. Problem solved?
        Before finding out the propane was gone, I had removed the condensate trap and cleaned it out. Thanks to a YouTube video I saw last year I knew it could plug up with crud. This time, however, it was clean so I put it all back together.
        One thing the Bryant manual says very clearly is that the trap must be primed, and it has to be done by pouring a quart of water through the inducer and on out through the trap. I didn’t do that last year and everything worked OK, so I didn’t do it this year either.
        Well yesterday I was pretty much out of ideas. I didn’t want to disassemble the inducer because I figured I at the very least I would destroy a gasket. So, I decided to prime the trap. Ever since, the burner has started. I haven’t always been there to see if it goes on the first try, but it has not gotten to the “4 tries and you’re out for 3 hours” fault at any time. Could the lack of priming really be the problem in this case?

      3. Hi Mr. Larsen! Great to hear that you got your furnace fixed. Yes, my Bryant 90I furnace instructions say the same, to prime before operating. I cleaned the trap and drain line on my furnace and did not prime the furnace and it worked. The only thing that I can think of is that maybe you flushed something out when you primed your furnace. Just glad that it is working. I hope this post will help others with your problem. Thanks so much for posting! Steve

  37. My furnace has begun turning off every morning around 7 am. It remains off until I flip the electrical power switch off and then back on, at which time the furnace starts right back up and functions just fine until the next morning at 7 am, when it turns off again. The thermostat is not set to make any automatic changes at that time. What do you think is going wrong?

    1. Hi Lori! Most of the time and the most common problem when I see this happening is when the furnace cools down during the night and the furnace has trouble sensing the flame because it is cold. I would suggest that you try to clean the flame sensor with steel wool or fine emery cloth. We have a flame sensor troubleshooting page that I hope will help: The furnace tries to light 3 times and if it does not sense the flame the furnace goes into lock out until you reset it with the power switch. If this does not work then you might need a new flame sensor. Please send me your furnace model number if you want me to look up the flame sensor your furnace uses. Most of the time the cleaning will solve the problem. Hope you have a blessed day and weekend! Steve A.

  38. i have a dukane 70,000 btu furnace in my small 2 br cottage about 800-1000 sq ft. my furnace starts running and runs for about 2 1/2 to 3 minutes and shuts off. about 8 minutes later starts and does the same thing. It will not run long enough to reach the desired temp i have set. I have three vents in living rm and one in kitchen, bath and both bdrms. I shut two vents in living room and temp seems to be holding but still kicks on every 8 min and runs for about 3 min and shuts down. I wonder if it is the pressure switch which seems to be a problem i am reading about on the internet that it is common to have to replace pressure switch. Please help if you have any idea.s

    1. Hi Mr. Sass! You would need to find out what control or safety device is causing the furnace to kick off after 3 minutes of run time. This could be something as simple as low batteries in a thermostat or a weak capacitor on the blower motor that causes the blower to run slow and kick the furnace off on high limit. I would suggest that you test with a volt meter set to volts AC. As in the furnace troubleshooting flow chart that we have on the following page: It says in one of the first steps: are you getting a constant 24 volts AC between W and C on your control board? If you are losing voltage between W and C then you have a thermostat problem. You might need to adjust the anticipator on the thermostat if equipped. Next I would suggest testing the limit to make sure it is staying closed during the time the furnace kicks off. If the limit is opening up then this means the furnace is over-heating which could be caused by a slow blower (might need a new capacitor), a stopped up AC evaporator coil, a dirty filter or blower wheel or too much gas input. Yes, the pressure switch could be the problem, but it is very unlikely the problem since your furnace is running for 3 minutes before it shuts off. More than likely something else is shutting the furnace off. Please go through the troubleshooting flow chart and let me know if I can help you out more. I hope you can easily find and fix the problem. Steve

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