Some common RV furnace problems can be solved with basic troubleshooting and simple repairs. Pilot Light Won't light or stay lit.
Make sure the thermocouple is positioned properly in the pilot flame
A common problem is a bad regulator at the propane tank. A simple test will indicate if this is the case. Light all the stove burners and look at the color of the flame. The flames should be blue with little or no yellow color. If the flame does not change color then the regulator is probably working. A bad regulator could also cause problems with the hot water heater.
Fan doesn't run and no heat.
If the fan will not start you should first check the thermostat. Remove cover and look for the "anticipator" adjustment. It will be an adjustable control with a sliding contact over a straight bare wire or a bare wire wound about an insulating material. If the fan will not start set the temperature to maximum and then move the anticipator slider while listening for the fan to start. Be sure to wait long enough... it normally takes our furnace 30 to 40 seconds for the fan to start once the thermostat sends a signal.
If the fan starts after you move the slider then you have probably found the problem. In this case you may find a slider position near the original position that will work reliably. If your thermostat anticipator adjustment uses the straight wire design and the wire lies directly on the plastic housing then you should look to see if the wire has sunk into the plastic. This wire produces heat and causes the wire to sink into the plastic and the slider no longer makes contact. It may be necessary to replace the thermostat.
Fan runs but no heat.
If your furnace fan starts you can assume that the thermostat is working.
Possible problems are insufficient air flow through the furnace or a bad regulator at the propane tank.
A furnace contains an internal sail switch, that senses the air flow. If the air flow is not sufficient then the switch will prevent the furnace from igniting and the fan will run but you will get no heat. Check to see if any heat registers are closed or blocked. Some furnaces will not tolerate even a partial closure of a heat register. A low voltage condition may cause the fan to run too slow to activate the sail switch.
If you have an electronic ignition check to see if the two contacts are touching or are too far apart. They should be about 1/8 apart.