I had a similar problem with mine. Is it a Suburban?
My problem was it suddenly quit after running on propane for weeks. It would work fine on electric.
It had propane to the valve on the heater, it had 12v to the valve on the heater and the valve was clicking when it was trying to start. The problem was a defective valve. It just stopped working one night.
I'm still under warranty and my dealer got me a replacement valve and I did it myself since it is easier than towing to the dealer. This replacement took about 10 minutes.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof