ATWOOD Furnace 8531

Either a stuck sail switch or the motor not generating enough RPM's to move sail switch. However you will find the service manual at
http://bryantrv.com/docs.html#furnace

Clicky: http://bryantrv.com/docs.html#furnace

If you can hear the ignitor snapping, then most likely the gas valve is not opening. If the igniter is not firing, then the sail switch or motor speed is suspect. The first thing to try is removing and reseating the wiring connector at the ignitor board a few times to clean up the contacts. Sometimes that's all that's needed.

Mine has that problem after it has not been used for a time have to turn it off and on several times to purge the air out of the gas line. It will try and light 3 times then just the fan will just run. Turn off at thermostat and have to start over till it keeps going with the burner going.

Ours does this like John Wayne said. If it doesn't start you might take your air compressor and blow air around the motor, the heater part, and the control board, anything in that area. After I do that mine goes back to running correctly.

Check the battery. Might need to be charged.

I had problems with mine, the same model. It is normal for the furnace to keep running after failed ignition. Turn the furnance on and go outside and listen for the ignightor to try to light. It will sound kike a clicking noise. The furnance will run for a couple of minutes, then the ignightor will try to light. It will try 3 times I beleive before it will stop trying. If it is clicking I beleive your board is good. I would pull the burner out and make sure no dirt dabber nest are in there and the orfice is not clogged. On mine after replacing everything and still not working I found inside the screen where the flame is was a small metal tap bent up and was not letting the gas get to the ignightor., bent the tap down and works great. If it is not clicking, it could be several problems, sail swithch, ignightor, gas valve, or board. The sail switch and gas valve can be checked with a meter. Visually inspect the ignightor, and if all else checks good replace the board.

Update to furnace problem. After changing my LP regulator the furnace started working again. Thanks for all the help.