Solution: First, turn off the power to your furnace. Check all wires and ground wires to make sure they have good tight connections and are not burnt. Next, remove the screw or screws that hold your flame sensor in. Please do not confuse the flame sensor with an Ignitor. We do not want to touch the ignitor at all. If you touch an ignitor it will shorten the life of the ignitor or it will break. Below this paragraph, we have a picture comparing an ignitor with a flame sensor. Clean your flame sensor with steel wool or emery cloth (fine sand paper). You might need a new flame sensor, but most of the time they can be cleaned and your furnace will work well after cleaning. I have seen the flame sensor go out. Most of the time when they go out the white porcelain is cracked. You might want to have a spare flame sensor on hand. Here is a link to our Flame Sensors Page: Please click here to go to our Flame Sensors Page or you can click on the flame sensor picture below. Near the bottom of this page, we have two YouTube videos on how to troubleshoot, clean and change-out a flame sensor. I have also experienced pressure switch problems that cause the furnace’s flames to go off after only a few seconds. If you are still having problems after cleaning or replacing the flame sensor then I would suggest that you test your pressure switch to make sure the pressure switch is staying closed during furnace ignition. Please click here if you are interested in seeing our furnace pressure switch troubleshooting page.
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Below is a picture to help you identify what a flame sensor looks like and what an ignitor looks like. Below is a picture comparing flame sensors on the top with an ignitor on the bottom. We do not want to touch the gray glass part of the ignitor or it will shorten the ignitor’s life or it might break.
Below we have a YouTube Video on how to troubleshoot and clean a flame sensor:
Below we have a YouTube Video made by AC Service Tech which shows in detail how to troubleshoot a gas furnace’s flame sensor. Thanks to AC Service Tech for making this great video!