While I agree that a digital thermo is a better way to go, I personally don't think that that is your issue. Have you checked the propane tank? How old is the regulator? I had this on our 2010 Niagara, and it was actually the connector that threads onto the tank. In my case, both of the connectors' check valves were no good, and were kicking the propane flow off and on. How is the stove and/or water heater affected when the heater goes off? Pay attention to what those items do at the same time. If they also shut down, it is not your heater, but a propane supply issue. That could be an empty propane tank, bad regulator (my local RV shop said those have a shelf life of ~5-7 years), or those connectors post-regulator that connect the regulator to the tank. Good Luck!