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Problem: Gas furnace will not ignite the gas to produce heat for our home. What could be the problem?

broken ignitor

Problem: The gas furnace will not ignite the gas to produce heat for our home. What could be the problem?

Answer: Your furnace probably has a bad ignitor.  The following sequence of operation is what I see most of the time when an ignitor is bad.

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 lockout 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.
Solution: You probably need to purchase and install a new ignitor. Please click here if you are interested in seeing the furnace hot surface ignitors we sell. I would suggest that you inspect your ignitor closely for cracks. Make sure you do not touch the ignitor (grey glass black part) with your bare hands. You can handle the ignitor by the white porcelain base of the ignitor.  If you do not visibly see a crack then you can test the ignitor with an ohmmeter to see if it is good or bad. Set the multimeter so it can properly measure the resistance of 10 to 200 ohms. Disconnect the hot surface ignitor from the control board and measure the resistance. A good hot surface ignitor will have a resistance of 40 to 90 ohms. Greater than 90 ohms indicates a failing or failed hot surface ignitor. Please see the video below which shows how to test an ignitor with an ohmmeter. If the ignitor looks and tests to be good then you could have a furnace control board problem or a limit, rollout switch, or pressure switch problem.  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 I would suggest that you clean your flame sensor with light sandpaper (emery cloth) or steel wool. You might need a new flame sensor, but most of the time they can be cleaned and will work well after cleaning.  We sell flame sensors on the following page: Please click here if you are interested in seeing the furnace flame sensors we sell.  We sell hot surface ignitors on the following page: Please click here if you are interested in seeing the furnace hot surface ignitors we sell. We sell 56 different ignitors. Please send your furnace make and model number if you would like for us to look up the ignitor or other parts for your furnace. If you have a Bryant or Carrier furnace we will need the product number in order to look up parts. If you have a Rheem or Ruud we will need both model number and serial number.  Our email address is You can also leave a comment in the comments section below and we will respond to your comment ASAP. Below we have two really good informative Youtube videos produced by Fix It Home Improvement Channel and Repair Clinic on how to test, replace a furnace ignitor and flame sensor. Thanks to Fix It Home Improvement Channel and Repair Clinic for making these informative videos.

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4 thoughts on “Problem: Gas furnace will not ignite the gas to produce heat for our home. What could be the problem?

  1. Replaced ignitor and heat sensor, still wont kick on, exaust fan tries to start a little but wont

    1. Hi Lisa! This sounds like you either have a draft inducer (bad draft inducer) or a control board problem. I would like to suggest that you turn off all power to the furnace and check to make sure all wire connections are good and tight. I would also like to suggest that you use a volt meter to test the voltage that is going to the draft inducer. You should be getting 110 to 125 volts AC to the draft inducer all the time that your thermostat is calling for heat. If you are not getting 110 to 125 volts to the inducer then you probably have a bad control board relay and you will need a new control board. If your are getting 110 volts to the inducer and it is not running then you will need a new draft inducer. If you have and ECM draft inducer then you will probably need to call a service tech to find the problem. ECM motors are harder to troubleshoot. 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. Hope you have a Happy Easter! Steve

  2. Hello,
    I am having problems during step 4. I do not hear the hissing sound of the gas. The ignitor glows but since there is no gas it won’t light. The draft inducer continues to run and then the ignitor glows a second time but still no gas and subsequentially no ignition. The draft inducer motor then turns off and the furnace goes into lockout mode until I turn the power off and back on again. Is there any way to test the electric gas valve?

    1. Hi! This sounds like your gas valve is not opening which could be caused by a faulty gas valve a bad gas valve relay on the control board or an open safety control. Yes, you can test the gas valve with a voltmeter. Here is what I found when I researched this topic on Youtube: I hope this helps you find and fix the problem. Steve

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