Sounds like a sail switch issue. Unfortunately, you need to remove the unit from the inside to open it up and do any troubleshooting. Its usually screwed down with just a couple of screws. Remove any duct work, propane supply line and any electrical connections. I had to cut my electrical wires and then splice them back as there was no way to get to the inside of the furnace to disconnect them.
Progressive Industries EMS - Hardwired
Marineco Detachable Shore Cord
CRE 3000 Equalizer / Wet Bolt Kit
Equalizer 4 Point WDH
2016 Ford F250 6.2 Gasser
Air Lift Rear Bags w/ On Board Compressor