Hi Murman,
The ignition sequence is failing and after 3 tries it goes into a safety lockout condition. Shutting off the thermostat clears the lockout.
The most common cause is poor propane supply to the furnace. This can happen if you're running low on propane in one tank and the other tank is not open (or if you opened it too fast and the overflow protection activated). It can also be caused by problems with regulators or the pigtails from tank to regulator.
Check the propane tanks first. We have 40 pound tanks that weigh about 32 pounds empty; 72 pounds full. 30 pound tanks probably weigh around 27 pounds empty; 57 pounds full. The tank can still weigh quite a bit when it's nearly empty.
If you have at least one full tank, close the valve, wait about 15 seconds, and open the valve very slowly. If you open it fast, the overflow protection device may activate, cutting off propane flow. If the furnace doesn't light reliably, move the tank to the other side of the coach and try it there. If it works on one side and not the other, there's a problem with pigtail or regulator, or crossover hose.
It could be other things like insects building nests or other stuff getting into the air intake. Or low voltage to the furnace.
There's some additional informaton in our
Heating and Cooling Guide located in the manuals section of the forum. Furnace info starts on page 15.
Let us know what you find.