Easy furnace flame sensor repair, clean, replace, fix

Q. Mr. Hardware, my furnace will start to ignite, goes through some startup procedures but shuts down. After several tries, the furnace will run but I know something is wrong. Can you help? Bob in GPF

A. Bob, it sounds like the flame sensor is carbon-ed up.

The flame sensor is a very simple component. It is located above one of the burners, usually in the upper compartment of the furnace. Once you locate the burners, look for a single wire with a ¼” spade (push on) terminal. It will be on the flame sensor, which is held in place with one ¼” hex sheet metal screw.

Pull off the spade terminal and remove the screw holding it in place. The sensor is part porcelain insulator with a 2 to 4” wire that extends above the burner. Remove it and sand it lightly with 150 grit sandpaper or so, (I used a sanding sponge), to remove all the dark carbon off the wire. Once it is clean, it should work for a month or two until you can order a new one.

It’s such a small item, so easy to replace and yet so important for your furnace to function.