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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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*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. 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 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


28 thoughts on “Gas & Electric Furnace Troubleshooting Simplified

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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.

  11. 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

  12. […] contacts to start working. We have a page that I hope will help you out. Here is the link: I believe that Frazier Johnson is similar to a York furnace. I could be wrong, but if you want me […]

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