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Problem: How Do I Test My Gas Furnace Rollout Switch, Limit Switch, Pressure Switch and Flame Sensor?


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 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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