What is wrong with the furnace in my RV?

I have a 2001 Winnebago Minnie. I discovered that if I turn on my heat, it runs until it meets the desired temperature then shuts down. Everything is cool right? But then when it starts again as the temperature drops, It blows nothing but cold air. If I turn it off and back on this sometimes makes it work. Once again, it blows cold air when it restarts. This is a electric start propane furnace. I had plenty of propane. Any Ideas where to look before I spend money on a repair? I have a warranty but the deductable is $200. If I can fix it for under that it would be great.