We went to fire up our furnace in the Glendale 5er & nothing happened- no fan. Had a service man who does other work for us come out (he does not usually work on RV's) & we thought we pinned it down to the circuit board, (# 34109)?.we purchased another circuit board & he installed it & still does not work. We circumvented the thermostat by hooking the wires together by the furnace......no work either, so it is not the thermostat. When we bump the reset button the fan jogs a bit & stops. When we slide the thermostat button there is no movement on the fan. If we go around the board & send power directly to the fan it runs just fine. The red light on the circuit board flashed a code 4 times indicating a sail switch problem but it has continuity, so it is not that we believe. No problem with propane supply either. Any ideas of what it may be? We are running out of ideas!