RV Repair: 2004 Jayco toy hauler, jayco dealer, wall thermostat

Question
QUESTION: My heater wont fire but the fan runs non stop even if the tstat is in the off position.

Any ideas ?

ANSWER: Travis... thats a good question.
First make sure you have good voltage to the furnace, 12.5 vdc or better. Next find and cut the two t-stat wires where they come out of the side of the furnace. This should turn off the fan after a short delay and release it from lock-out....wait..
If the fan goes off, the problem is upstream toward the wall t-stat. It could be the thermostat or the wires leading to or from it. If the fan did not go off the furnace needs to come out for service.
If the fan went off, strip the two thermostat wires and connect them together, this will act as a temporary t-stat set on high "to test only". If the unit spools up and heats then look at the wall thermostat.    
If it us a dual mode (heat/cool) then you'll need to get help from a qualified tech....or you can try it yourself,but they can be sensitive and expensive... (thermostats and techs).
Good luck and don't let the smoke out.
Thom

---------- FOLLOW-UP ----------

QUESTION: Ok. I have a question. Before I go cutting wires.
I have the trailer plugged into 120v and I am sure I am getting good power. Heater runs on electric or lp. At this point lp will only fire for a couple minutes if I unplug it. When plugged in today I start uplugging every wire I can find and re plugging in. Out of the blue the heat starts working. Problem is fan doesnt shut off when to templ so it never starts again. Now if I go messing with the t-stat... off mode on mode temp up down multiple time it will wind up starting. I called the Jayco dealer here but he tells me to pull the furnace and bring it to him. I dont have the time or no how to go messing with this thing so I am at a loss of how to proceed.

Thanks for your help
Travis

Answer
Travis
The clues are pointing towards you having low voltage or a worn out fan motor.
Even plugged into 120vac a low voltage issue can occur.
When a furnace receives low voltage the fan will run but it will not push enough air to trigger the sail switch (a safety switch). The sail switch sends a signal to the board allowing the gas valve and the igniter to engage.
You'll need to determine the voltage at the furnace and the condition of the fan motor to solve the rest of the puzzle.
Thom