Atwood 7920-II furnace failure

trailrider wrote:
If you have the newer version with the fan relay on the circuit board you need to check for power from the fan terminal to the fan motor when the thermostat is calling for heat. And make sure the thermostat is closing the circuit between the two white wires on this diagram.

http://techsupport.pdxrvwholesale.com/wp-content/uploads/2017/08/Atwood-7920-II-Installation-Manual.pdf

Thanks for reply trailrider, this unit is about 20 years old so don't think it's a newer version. I'm not great at deciphering electrical diagrams, but can usually figure stuff out.
All roads seem to point to the control circuit board.

Unit is in a 06 Lance camper 855 we bought as old new stock 5 years ago. Was a trade in we bought from local dealer, the previous owner never used it, it was untouched like new throughout. Even through, all the appliances have had issues I've had to address except the stove which is analog, no electronics.