i have a train xl80 furnace. When it calls for heat the draft inducer fan turns on and then the burner fires up for a short time then shuts off then it starts all over again.I am thinking its the flame sensor. please help.

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    Does it have any indicators to show fault codes? Sure sounds like a dieing flame sensor, but it could be a loose connection or a bad board as well. – Tester101 Dec 22 '14 at 14:35

I just yesterday dealt with one like that. It had electric ignition (glowing ignitor) and a single yelloow "flame sense" wire. This is only the second one of these I've found in a decade, but the problem and the solution is the same. IF your unit uses ion flame detection, the burner ground has become oxidized. It may look like metal against metal, but a fine coat of invisible oxidation had formed between the metal parts. It needs a good "ground reference" before it can detect the ions.

To fix this, I removed the burner. While I had it out, I scraped the flame rod tip some but it wasn't really dirty. When I put it back in, I intentionally made one of the self-tapping sheet metal screws dig a new groove instead of putting it back in the first grooves. I also got it good and tight.

Just as in the first case, the mere act of disturbing the mechanical assembly caused a better ground to be formed. It must be working, because I didn't have to get up last night and go fix it.

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  • I think it was only from cleaning the sensor; it's (still and has always been) isolated from ground or you have defeated its purpose. – Mazura Mar 28 '15 at 23:54

It could also be a simple matter of the vacuum tube in the unit having some small debris in it. Mine does this now and then. You're talking about a power vent to the outside correct?

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