errolcw,
Give us a little more info on the type of RV, make of furnace, etc. If the fan runs, the ignition sequence starts and then main flame goes out, the likely cause is failure of the flame detector or a circuit board failure. Those are things that are getting into the realm of "Service Tech Required". Here are some things to eliminate from the list of possibilities.
Have you done the routine things like light a burner on the stove. That will tell you if there is propane available to the furnace. Make sure all the vents and returns are open and clear. Most RV furnaces have an airflow "sail" switch that will not allow the burner to operate with a reduced airflow. Most RV furnaces have no air filter. Check to see if one has been added. If so, remove it and try again. With the fan running, check to see if you can feel air flow at a duct register. A low coach battery may cause the fan to run slowly enough that the sail switch won't make.
Try those things and get back to us with more specific data and try to describe exactly what happens and when so we can get a better idea of what's going on.
Q
