I have a Rheem Classic 90 upflow heather. When it turns on the burner comes on fine but it stays on for just 5-10 seconds then shuts off. It does this twice then the blower comes on but with no flame going. The yellow flame sensor LED doesn't come on at any point. I have cleaned the flame sensor with steel wool. But apparently there is no power to the flame sensor. The two red LED's are on.
Any ideas?

Make sure you have a clean circuit to the sensor (not grounded), a solid ground to the burner assembly, and that all the burners are lighting.

Flame sensor could simply be shot.

Flame sensor could simply be shot.


It's $12 so why not try replacing it. It looks fine though. The furnace worked fine last winter. This was the first time to start it up this winter. But I guess no yellow light speaks to either a faulty sensor or a bad board.

Just replace it. I usually replace most flame sensors,unless I don't have one on the truck. You hate to have a call-back on a five dollar part. Check all of your connections.

Just replace it. I usually replace most flame sensors,unless I don't have one on the truck. You hate to have a call-back on a five dollar part. Check all of your connections.Have you tried to check THE FLAME RECTIFICATION CIRCUIT?