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Problem: How do I check to see if I have a bad furnace gas valve or a bad control board?

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Problem: My gas furnace’s draft inducer starts, the furnace ignitor glows but the furnace never gets a gas flame. Do I have a control board problem or do I have a gas valve problem? I have checked my pressure switch and the pressure switch is closing when the draft inducer is on. How can I test the gas valve and control board to see which part is at fault?

Answer: Thanks for asking this question. First, I would recommend that you test to make sure all your safety controls are closed and the safety controls are allowing electricity to flow through them. The safety controls would be the pressure switch, which you have already tested, the rollout switches, and the limit switch. If any of the safety controls are open then the furnace will not operate. We have a really good post and Youtube video on testing safety controls on the following page: https://arnoldservice.com/problem-how-do-i-test-my-gas-furnace-rollout-switch-limit-switch-pressure-switch-and-flame-sensor/ I would like to suggest that you make sure that the gas valve and the furnace’s gas cock are turned on. If you have an LP furnace make sure that the LP tank is actually filled well enough. Make sure that if your thermostat has batteries that the batteries are in good condition.  We have two really good YouTube videos below made by Gray Furnace Man that show how to test gas valves to see if the gas valve is getting power or not. If the gas valve is getting power and not opening then you more than likely have a gas valve problem. If the gas valve is not getting any power when it is supposed to be getting power to open then more than likely you have a control board problem.  Below are two great YouTube videos that explain how to test a gas valve with a clamp-on meter and how to test a gas valve with meter probes. Thanks so very much to Gray Furnace Man for making these videos! If you have any questions please comment below or email us at arnoldservice@gmail.com. We hope this helps you solve and fix your furnace problem. 

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