On ours, there used to be a delay once you turn it on... time for propane to flow, time for sensors to indicate heating, etc....
but like Scott said - check breakers - fuses... even if a breaker LOOKS ok, turn them off and back on to make sure !
Sounds like electrical, but to be certain it's not propane,
I would light the cooktop to ensure the gas is flowing and most of the air is out of the system.
(purging the system sometimes took a while for our 38gk, I would light a little bbq starter and hold it by the burner until it started rather than keep clicking the cooktop starter)
Once cooktop does ok, try heater again...
Do you have heat pumps on the roof ac ? do they work? if so, can use them until you resolve furnace issue...
That thermostat has SO many settings, just make sure it is set properly... good luck
Ours: '11 Monaco Diplomat 43DFT followed closely by '14 Jeep 4 dr Wrangler.
Hers: '13 Explorer Sport - AWD 365hp twin turbo scooter!
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