The LP furnace blower in my 2002 Winnebago Adventurer will not start. If the blower does not start the furnace will not lite. I think it is a voltage problem.
Might be an issue with your thermostat - if the prior owner upgraded to a digital thermostat then it might be as simple as replacing the battery inside the thermostat.
Edit: You should also note that your furnace fan won't operate if your coach batteries are dead/too low.