Cold air from my furnace

Hi everyone;

Just bought my first travel trailer and getting ready to hit the road as a full-timer. I am currently reading about all the things I am supposed to know about operating the different systems. I tried my furnace, worked real good for about half an hour then started to throw cold air. Tried again the following day, worked real good for a while then cold air again. I noticed that the furnace never stops. I thought it should after it reached the set temperature. Can anyone give me some advice on the matter. It will be greatly appreciated.

Re: Cold air from my furnace

Hello and welcome to the forum.
Your furnace won't cut off because it is not reaching the set temp. Why it is stopping after a half hour is a good question. My guess would be that something is overheating and cutting it off. You did not say what type of furnace you have, but a Suburban has a high limit switch. That could be it, but it could also be the board going bad.
Good Luck


Senior Member
Re: Cold air from my furnace

I had the exact same problem in my tent trailer and in my motor home. The dealer told me the tent trailer was a fuse and they kept replacing it and we kept having the same problem. My motor home they said it was a board and they replaced it and it has worked fine since. The service manager said that there is a device on the circuit board that goes out on a lot of them. Good luck to ya.


Senior Member
Re: Cold air from my furnace

Both the Suburban furnace and those from Atwood have a device called a "high limit thermostat" to prevent over heating and the dangers that could result. I tend to agree with Ken that this is probably what is happening to yours. There are quite a number of things that could cause this problem. Any restriction of the air flow through the heat exchanger could do this. This would be things like crushed heat ducts, or something covering one of your duct outlets. If it is the high limit device, it should close and reignite when it cools sufficiently. Have you left it run for at least 1/2 hour to see if it will start to heat again?

If it does not begin to heat again, then it would seem to have gone into "lock-out" which is a condition that is designed into the controls to shut down in a fault condition. That could be an electrical problem or it could be something like low gas pressure causing the flame to fail. It is very difficult to diagnose such problems without more information. Proper propane pressure is 11" of water column at the inlet to the furnace.

Try turning the furnace on and get it operating properly, then after 10 minutes or so, turn the thermostat to the bottom of the scale to see if that will cause it to turn off, as it should when the set temperature is reached. If it does, after a minute or two, push the thermostat back up to where it comes on again and see if it does so. If that works, try letting it cycle on and off for 10 to 15 minute periods to see if you can slowly bring the temperature up toward where you have it set. In this way you can determine if the thermostat and associated controls are working properly. If they are, check the air flow from all heat ducts. If there are any that do not supply heat, trace the duct work and make sure that none is blocked or crushed, restricting air flow.

If there is some problem with the circuit board, it can be difficult to detect. There is also the possibility that the gas valve is failing.
Re: Cold air from my furnace

Thanks very much for the information. I am gone for the week-end but as soon as I get back I'll check it out and get back to you.

Thanks again. Rena