Furnace running even with thermostat off

[allan3089]

Hi folks:
I recently purchased a 13' 2002 Trillium Outback trailer (Yayyyy!) and I just came back from my first week away. I have a niggly issue with the furnace (Suburban Model NT-12SE) in that although it seems to run just fine most of the time I found that when the outside temperature hits freezing, or close to freezing, it starts up automatically - even when I've set the thermostat to the "Off" position.

I thought with the stat set to off it shouldn't run at any time, regardless of the temperature? This only happens when it's really cold and I'm wondering if this could be a problem with the thermostat or possibly with the furnace??

Since I store it during the winter I don't want the furnace to run every time it gets close to freezing, so until I figure it out I'll have to disconnect the battery.

Any ideas ? I was going to change the thermostat, but maybe there's another reason why this is occurring?

Thanks for any help you can provide
Al

[Byron Kinnaman]

The problem is probably in the thermostat.
I've had thermostats that are hard to get turned off. When the lever is pushed to lowest setting there's some resistance which you go beyond to turn it off. Some thermostats have more resistance at that point than others. If should need to replace the thermostat it's not difficult nor expensive. I think I paid less that $5.00 each for the ones I purchased. I think I bought 2.

Take the cover off, it just pulls off, and look where the lever is when it all the down. There's a couple of brass pieces that the lever should go between to shut of the furnace completely.

If you're still worried about it while in storage, you can remove the battery that powers the lights and other 12 volt things, you can find the right fuse in the fuse panel and remove it. WARNING If you remove the battery write down which wires went to which terminal. Many things have been destroyed by connecting a battery backwards.

[Raspy]

It might have a freeze protection setting somewhere. Maybe the thermostat doesn't have an "OFF" position that means totally off. Does the t-stat have an off setting or is it just pushed down to the lowest heat setting? Test it by disconnecting the wires at the t-stat. If that shuts it off, you know the stat is the culprit. If it still runs, it has a freeze protection mode in the heater. If you will be leaving it somewhere, just switch off the breaker that runs it.

[Jack L]

Check on the bottom of the thermostat to see if there is an additional on-off switch. My Bigfoot came with one.

[allan3089]

Originally Posted by Raspy

It might have a freeze protection setting somewhere. Maybe the thermostat doesn't have an "OFF" position that means totally off. Does the t-stat have an off setting or is it just pushed down to the lowest heat setting? Test it by disconnecting the wires at the t-stat. If that shuts it off, you know the stat is the culprit. If it still runs, it has a freeze protection mode in the heater. If you will be leaving it somewhere, just switch off the breaker that runs it.

Raspy - I think you nailed it. I did disconnect the wire at the stat and the furnace didn't run again during the cold night hours. It's just the plain Suburban thermostat and it definitely has an "Off" position with a small detent (notch) that seems to click into position, but doesn't seem to work - at least when the temperature is close to freezing. I will change out the thermostat as they're cheap and give it a try.

Thanks for all the suggestions - much appreciated!
Al

[Franswa]

my thermostat has an on/off switch, a small tab, on the bottom of the stat...(with no markings on the front of the cover...the arrow and "on" were added by me in pen)

could it be that your tab broke off and you actually have that switch but now have no way to move it to the "off" position? !!...worth a look

[stude]

Originally Posted by Franswa

my thermostat has an on/off switch, a small tab, on the bottom of the stat...(with no markings on the front of the cover...the arrow and "on" were added by me in pen)

could it be that your tab broke off and you actually have that switch but now have no way to move it to the "off" position? !!...worth a look

:
If you look at your thermostat there is high and a low and low is about 55*F so when it gets that low the furnace will come on usually start short cycling all night long trying to keep the temperature up to that low point. All the units I have had have a shut off switch so when I hit the sack I just shut it off so I do not have to hear it all night.
Stude

[Franswa]

"when I hit the sack I just shut it off" .....and THAT'S why they call it camping....

yeah, I do the same....once I found the right temp. setting (top scale) I never touched it again....just use the on/off switch....

[allan3089]

Just an update - I took off the old thermostat, drilled out the rivets holding it to the cupboard wall and installed a new Honeywell non-programmable digital thermostat. Took about 1/2 hour and tested it out and it seems to run fine. Will have to wait for cold weather, but I'm sure it'll be fine. This one has a separate off switch so that's what I'll use when I don't want it to run at all, regardless of the outside/inside temp.

Appreciate all the help - I'm new to FG trailer repairs, so I know I'm going to have more questions along the way. Hope I don't become a pest.

Al

[tony in nanaimo]

I may be a day late and a dollar short , I'm not sure of the internal workings of this thermostat but it could be a unit with a ball bearing or mercury and must be fairly level , eg. trailer floor must be level and thermostat square with the floor or you can have the problem you described ; )
Tony

[Gerry]

Originally Posted by tony in nanaimo

I may be a day late and a dollar short , I'm not sure of the internal workings of this thermostat but it could be a unit with a ball bearing or mercury and must be fairly level , eg. trailer floor must be level and thermostat square with the floor or you can have the problem you described ; )
Tony

There are 2 types of thermostates, one will work with a bi-metal spring with will react to temp and the other is mercury in a tube type.
The mercury in a tube type should hang level as the mercury sliding to one end of the tube when temp rises of falls, makes contact with tabs inside tube to complete low voltage feed to furnace. If "OFF" lever is there and turned to OFF the tube is tilted so far as the mercury can not make contact.
Bi-metal type looks like a spring with will expand and contract opening or closeing the points to make contact
If a thermostat has a true "OFF" lever it will either usually push the points, via a wedge, far enough apart so contact can not be made.

[Raspy]

Best thing to do is run the digital ones because they have a temperature readout, or the magnetic leaf type if you don't want the batteries that the digital ones require.

Not the mercury one or the rolling ball one because they will constantly be making and breaking contact as the rig goes down the road.

[Dan Meyer]

There i also a switch on the right side of the furnace inside a hole that is about 1 inch in diameter. In my camper, you can't see this switch without a mirror, but it is there. If you want to be certain your furnace is off, flip this switch to the off position. Don't forget to turn it on when you want heat!

--Dan Meyer