Atwood 8500 Furnace
Working on a Friends furnace. Here is the issue. -turn the thermo on for heat and the furnace starts -fan spins ignitor sparks and gas flows -you can feel heat at the exhaust -after about 10 sec...
Forum Discussion
If the sail switch was the problem it would have never lit. The problem soumds like there is no flame recognition so it shuts down. Find the flame sensor and take some fine grit sand paper to it and clean it up. Just as in residential gas furnaces if the flame sensor is rusted up it cannot sense the millivolt signal carried from the flame. Sounds weird but that's how it works. Shine it up like a new dime and see what happens. There is a sequence of events that have to happen to get the gas valve to open. If it was the sail switch then it would have sensed no air flow and would have stopped the ignition process. Sand down the flame sensor, its just a metal rod. Now your spark ignitor may also double as the flame sensor. If that's the case, sand that down but becarefull not to increase the gap between the electrodes
