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Flame Sensor a simple fix for a very common gas furnace problem

It's 11:00 PM and 15 Degrees outside and your furnace is acting up... That's just great! you say to yourself. Now I have to call an HVAC Contractor and pay hundreds of dollars extra to get my furnace fixed or freeze the rest of the night... Wonderful!

Well sometimes the most common gas furnace issue does not have to cost anything to fix and you would be surprised at just how easy it actually is to resolve the problem. What are we talking about here? The flame sensor.

The flame sensor is usually a small metal cylinder about half the width of a pencil and an inch or two long and will have a long wire or metal tube connected to it. The sensor will sit or be positioned directly in the flame itself... when it is lit of course and the sensor tells the control board that you have an active burner or pilot flame and when it is not working properly it will cause a nuisance by allowing the furnace to run sometimes, sometimes for short periods and sometimes not at all.

The problem is very common and can sometimes be rectified by simply cleaning the little metal probe that sticks in the flame. These metal probes are prone to getting caked with a deposit, usually an off white or brownish rusty color. This cake of crud prevents the sensor from heating up properly and provides the control board false readings for the flame condition.

So if you are stuck in the middle of the night with the gas furnace symptoms described above you can try this simple measure and see if it works. Simply clean the metal cylinder with fine sandpaper or emery cloth, you can also use steel wool or other fine abrasive materials. Just clean it enough to get that caked crud off... just be careful not to scratch off too much of the metal as that can ruin the sensor.


This works nine times out of ten and this same procedure can be used on many gas water heaters when the pilot light that will not stay lit as it is pretty much usually the same problem. If the sensor is clean and the gas furnace or gas water heater still does not work then it is more than likely time to call Ameri-Serv Heating and Cooling for a furnace repair or water heater repair.

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