Problem: My gas furnace’s ignitor will not glow, my electronic ignition will not spark and my gas furnace will not ignite the gas.Steve, You told me to make sure that all my safety controls are closed before testing the control board and other components for problems. Where are the furnace’s safety controls that you are referring to and how do I test these controls to make sure they are working correctly?
Answer: We have this question asked a lot. For the gas furnace to operate the safety controls like the rollout switches, limit switch, and pressure switch have to be closed and allow the 24 volt AC current to flow through the controls. If you have an open safety control then your furnace will not operate. The safety controls are installed by the manufacturer’s engineers to prevent a fire and possible carbon monoxide poisoning. The flame sensor has to sense the gas burner flame and send microamps back to the furnace control board telling the control board that there is a flame. No flame sensed by the flame sensor then within 8 to 10 seconds the flames cut off. No heat! We have an excellent YouTube video made by AC Service Tech LLC below that explains how to quickly test and troubleshoot these safety controls. If you find out that you need a rollout or limit switch then please click here to see the rollout and limit switches that we sell. If you test and find out that you need a pressure switch then please click here to see the furnace pressure switches that we sell. If you find out that you need a flame sensor then please click here to see the flame sensors that we sell. If you have any questions or if you would like for us to look up parts then please send us your furnace’s model number by email at firstname.lastname@example.org. We will be glad to try and help you out. Please comment below if you have any questions or comments. We would love to help you out and earn your business!
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Problem:My Gas furnace will not heat or work. What furnace parts might be the cause of this problem?
Answer: We have this question asked lots. There are 6 main parts that can cause your furnace to not heat. Some of these parts can be blamed or misdiagnosed as bad when actually the part is good. The only way to find out if the part is bad or not is to do some testing. Below we have a really good super YouTube video where AC Service Tech LLC shows and explains what the 6 most frequently misdiagnosed parts are and how to test them. I have listed below the video many troubleshooting links where AC Service Tech explains how to troubleshoot each furnace part in detail. There are also links to the troubleshooting tools that AC Service Tech uses in the video. Thanks so very much to AC Service Tech LLC. for making these excellent informative videos!!
The 6 parts that are blamed and misdiagnosed most often are:
Flame Rod or Flame Sensor- Usually cleaning the flame sensor will fix the problem.
Gas Valve –AC Service Tech LLC has testing and troubleshooting links to YouTube Videos below.
Pressure Switch-AC Service Tech LLC has testing and troubleshooting links to YouTube Videos below.
Control Board-AC Service Tech LLC has testing and troubleshooting links to YouTube Videos below.
Blower Motor is bad or on High-Efficiency furnaces, the ECM Blower Motor is diagnosed as bad-Many times a motor run capacitor can be replaced on PSC (Permanent Split Capacitor) blower motors and it will fix the blower motor problem. Most of the time the ECM motor module is bad and the motor is not actually bad. Replacing the motor module is less expensive than replacing the entire ECM motor. AC Service Tech LLC has testing and troubleshooting links to YouTube Videos below.
Heat Exchanger is bad. If one of your rollout switches is going off where you have to reset the rollout switch then this is a sure sign that you have a heat exchanger or venting problems. Make sure your condensate drain is open and your vent is not obstructed if you have a 92% or above condensing furnace that produces water during the winter.
Problem: My gas furnace will not turn on? Nothing happens when I turn the heat up on my thermostat to start my furnace. What could be the reason that my gas furnace will not start?
Answer: We have this question and problem asked many times. I have had this problem with my own furnace over the years. Below we have a great YouTube video made by AC Service Tech LLC that explains 8 reasons why that a gas furnace will not turn on. Many thanks to AC Service Techfor making this excellent troubleshooting video! Here are the 8 short reasons why the gas furnace will not turn on. If you would like an explanation of the reasons I would highly recommend watching this 12-minute video.
Reasons why a gas furnace will not turn on:
No power to the furnace. Make sure that you check the power switch, the circuit breaker, and the door safety switch to make sure they are all on. You can tape the door safety switch down so the furnace will be on and check with a voltmeter set to “Volts AC” to see if you are getting power between L1 and neutral wire on the control board. You should be getting between 110 to 125 volts AC between L1 and neutral.
Problem: I turned my thermostat up to try and get my heat to come on and nothing happens! My furnace’s draft inducer will not start. After 30 seconds to a minute, I get a flash code on my control board that shows, “Pressure Switch Failed to Close”.
Answer: We have this question asked quite often. The first component of the furnace that should start up after the thermostat is turned up to call for heat is the draft inducer. It might be necessary to tape your furnace’s safety door switch closed temporarily so you can test the furnace’s control board with a voltmeter. Test with a voltmeter on your furnace’s control board to make sure you are getting 24 to 28 volts AC between the W and C (com) thermostat wires that come from the thermostat. If you are not getting 24 volts between W and C (com) then you either have a thermostat problem, a thermostat wire problem, the thermostat might not be turned on heating or turned up, you could have a low voltage transformer problem or a blown fuse on the control board. Make sure that the batteries in your thermostat are in good condition. If you are getting 24 volts between W and C (com) and the draft inducer is not coming on then please watch the following really good YouTube video made by AC Service Tech LLC. Craig Migliaccio on “How to tell if a draft inducer motor is bad”. Please click here if you would like to see many air conditioning and heating videos made by AC Service Tech. I believe these are the best HVAC Repair Videos on the Internet! I hope this post will help you in finding and fixing your furnace problem! If you have any questions please comment below or email me, Steve Arnold at Support@arnoldservice.com. Thank you so much for your time and support with our website!
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This excellent Youtube Video made by AC Service Tech LLC that explains why it is important to know the Gas furnace sequence of operation when troubleshooting furnaces. If one sequence of operation does not occur then as a troubleshooter you can focus on the sequence that is missing and fix the problem. Thanks so very much to Craig Migliaccio for taking the time to make this excellent video! I have the sequence of operation below. The YouTube video illustrates the sequence of operation on a Bryant Carrier 92% condensing furnace. The proper sequence of operation is:
The thermostat calls for heat by the home owner (you) turning the thermostat up.
The thermostat provides 24 volts to the W terminal on the control board. When you check with a voltmeter you should have 24 volts AC (alternating current) between W and C (com) on the control board.
The control board sends 110-125 volts AC to the draft inducer to start the draft inducer.
If the vent and combustion chamber are open then the pressure switch closes the connection between the two wires that go into the pressure switch. If the furnace pressure switch, limit and rollout switches are all closed (allowing current to run through them) then the control board starts the furnace ignition sequence.
The control board sends power to the furnace ignitor which should glow bright orange for a set number of seconds. Usually 15 to 30 seconds. During the set time that the ignitor is glowing the control board sends 24 to 28 volts AC to the gas valve to open the gas valve allowing gas to flow and the gas burners to ignite (start burning). If the gas burners do not ignite in 5 to 8 seconds the flame sensor does not sense the flame and the control board turns the gas valve off. FYI-If this happens you might need to clean your flame sensor or replace your flame sensor. Please click here if you are interested in the flame sensors we sell. If the flame sensor does sense the flame the control board sends 24 volts to the gas valve and the gas burners continue to burn until the thermostat is satisfied.
After the furnace gas burners ignite the furnace, the furnace’s heat exchanger heats up for approximately a minute or so then the furnace blower comes on to distribute the heat throughout your home.
The furnace blower motor and gas continue to burn until the thermostat on your wall satisfies the need for heat (reaches the set temperature) then the thermostat breaks the voltage in the W (white) wire and cuts the gas burners off.
The furnace blower motor continues to run for a set amount of time that is determined by the furnace’s control board until the heat is removed from the furnace’s heat exchanger. Then the blower motor goes off until the next heating cycle from the thermostat on the wall is needed. If you have any questions please contact us anytime. Our email address is:email@example.com
We Would Love to Help You Out and Earn Your Business! Steve & Barbara Arnold
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Problem: Draft inducer will not start, ignitor will not glow or gas valve will not open. I think my furnace’s draft inducer is having problems?
FYI: *You would be surprised how many people go without heat or cooling for hours/days and all the problem they have is the switch on the side of the furnace is not turned on or the blower door is loose after they change a filter! One customer blamed his cat for turning it off! LOL! I try to go over this with my customers before I make a service call so I do not waste their money.
Solution: Any combination of the above problem or problems could be caused by a bad furnace control board or bad draft inducer. I always troubleshoot and test the least expensive parts first, such as the thermostat, 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. We have two really good Youtube videos below that show the 8 top problems when a furnace draft inducer will not start. This excellent video was made by acservicetech. Thanks to acservicetech for making this great video!
We have another really good YouTube Video made by Word of Advice TV which covers the following information:
Is your inducer motor not turning on? Or perhaps the inducer motor is noisy or stuck? Does not shut off or turns on and off? All of these question are covered in this video along with inducer motor troubleshooting, testing, and checking. Here is a little summary of what is covered in the video: 1. Noisy Inducer Motor 2. Stuck Inducer Motor 3. Inducer Motor Not Starting 4. Checking Voltages on an Inducer Motor 5. How to Check the Capacitor 6. How to Check Resistance 7. Inducer Motor Running Nonstop 8. Inducer Motor Turning On and Off Thanks so very much to Word of Advice TV for making this excellent troubleshooting video!
1. The first thing that is supposed to start when a furnace starts up is the draft inducer. If the draft inducer does not start then you probably either have a thermostat , thermostat wiring problem, electrical problem, control board problem or a bad draft inducer.
2. Tape the blower door safety switch shut (if equipped) and set your thermostat so it is calling for heat. Us a volt meter set to “Volts AC” and test between terminals W (usually white wire) and C (Com) and see if you are getting 24 to 28 volts between these two terminals. If you are getting 24 to 28 volts between the W and C terminals then your thermostat and thermostat wiring are in good shape and doing what they are supposed to be doing. If you aren’t getting any voltage then you might have a bad thermostat, bad thermostat wiring, not getting 110 volts to the furnace (make sure switch on furnace is flipped on and blower door safety switch is pushed in) or a blown fuse on the control board. We have a picture of a fuse on the control board below. Most of the time you can get these fuses at a local hardware store. You would be surprised how many people go without heat or cooling for hours and days and all the problem they have is the switch on the side of the furnace is not turned on or the blower door is loose after they change a filter! I try to go over this with my customers before I make a service call. If the fuse on the control board is blown this usually means that you have a short in the low voltage circuit of the furnace. Most of the time I find that the animals have chewed through the thermostat wires and shorted them out or the thermostat wires over time have been pinched around the body of the furnace or air handler which has caused them to short out. You will probably need to replace your thermostat wire if you find it has shorted the fuse out. If the fuse does not fix the problem with the low voltage then you may have burnt out the transformer. We sell some transformers on the following page: Please click here if you are interested in seeing the transformers we sell. You should have a constant 24 to 28 volts AC between the R (red) and C (com) terminals on the control board no matter how the thermostat is set. This is the power coming right off the low voltage transformer. If you do not have 24 to 28 volts between R and C then you probably need a new transformer.
3. 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: If you find that the control board or draft inducer is at fault we sell many different types of control boards and draft inducers. Please send us your furnace’s model number and we will be glad to look it up and see which control board or draft inducer your furnace uses. Our email address is: firstname.lastname@example.org
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 you get tired of burning up fuses we have a tool called the LiL Popper that has a button you can push in when the fuse blows instead of having to throw away fuses. We sell the Lil Popper on the following page: Please click here if you are interested in seeing the Lil Popper tool that we sell.
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. Please email us or comment below if you have any questions. Our email address is email@example.com
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