Furnace help needed please

[lakedawgs]

Hello,
Getting ready for a weekend trip I decided to run the furnace for a while to  'wake it up'.
I have a 2000 Nomad 25'TT. The furnace was run for 2-3 hrs when I bought it in April but not since. Worked fine then.
It fires up fine and blows hot but after about 20 minutes the heat goes away and the exhaust vent outside cools off. Obviously the 'fire' is going out. I can turn off the furnace at the thermostat, wait a minute, and turn it back on and the heat comes back on fine.
The blower keeps running but no heat. I have plenty of propane.
Any ideas?
THANKS,
Lakedawags

 

[Gary RV_Wizard]

Sounds  to me like the high heat emergency cut-off is doing its thing.  If the furnace gets too hot internally (in the heat exchanger), it will cut off the burner. Shutting it down and restarting will reset it.

There is a Furnace Troubleshooting document in the forum library - take a look to familiarize yourself with how the furnace works and what can go wrong.

 

[lakedawgs]

Thanks Gary,
I have done some reading and kept an eye on it last night. I let it sit for an hour and then restarted. It ran fine for 20-30 minutes then shut off.
We plan to use a small space heater this weekend and will not be 'testing' the furnace any more.
Once we get back in town I will remove the covers on the furnace and blow/clean it all out.
THANKS,
Lakedawgs

 

[utmtman]

When I bought my motor home I had the same problem, but after a year of that I found out that I had a circuit board that was bad.  They replaced it and have not had a problem since.

 

[Lou Schneider]

Make sure nothing is obstructing the airflow in or out of the furnace.  If a duct or a register is closed off it can reduce airflow through the furnace enough to trip the overtemp switch.

The same holds true for a marginal battery.  If the battery is really low, the blower won't turn fast enough to activate the sail switch when you start the furnace, and the burner won't turn on.  But there might be a point where the battery has enough charge to activate the furnace, but the voltage might not be high enough to force enough air through the blower to keep the furnace cool after it starts running.