furnace won't shut off

dwesol

I came home from an overnight trip to find the temperature in my condo a toasty 104 degrees. I shut off the breaker for the furnace and set the thermostat to the OFF position. When I turned the breaker back on, the furnace stayed off, but if I put the thermostat back into the AUTO position, the furnace kicks on again immediately. Is it safe to say I have a bad thermostat or are there other things I need to look at? That seems like the obvious issue, but before I go and buy a new thermostat, I thought I would ask someone with knowledge in this area.

My thermostat is a White-Rodgers Model #1F78

Any help or troubleshooting tips would be appreciated!

Thanks!

HvacWiz

Is this an electric or gas furnace?

UBoiler

I bet a HVAC pro out here could tell you in a short paragraph the smartest and easiest way check a thermostat to see if it's at fault. I actually would like to read that paragraph. Thanks Cliff

dwesol

The furnace is gas.

More info on the issue:
I had the thermostat shut off until the temp in my condo got down to 55 last night. The thermostat is programable, and in the evenings at 11:30pm it is set for 65 and then it goes up to 72 at 6:00am. When I turned the thermostat on at 11:45 the furnace kicked on and warmed the place to 65 and shut off. It worked correctly throughout the night and kept a constant 65 degree temperature. When the temp setting adjusted to 72 at 6:00 am, the furnace kicked on and went past the 72 degree mark and I had to shut it off manually at 75. So it seems that it works fine for temperatures below 70, but once the thermostat is set above 70, it will not shut off. Has anyone experienced this before? It doesn't make much sense to me. I am afraid to leave the furnace on at all (at any setting) when I leave for work because I fear it's going to kick on and keep running all day. The high is going to be in the mid 20's today, so I don't want to leave it off altogether, but I don't want to come home to 100+ temperatures again either.

Any suggestions? I am going to buy a new thermostat today, it seems like the only obvious answer. If there is anything else I am overlooking, please let me know. I will post the results after I install the new one.

NateHanson

You place isnt' going to freeze up in a day, so I'd just shut it off when you leave, and go pick up a new thermostat. That's what it sounds like to me (a lowly homeowner).

Or keep it set in the 60s since it seems to work at that setting.

redline

Start with the thermostat.

The other possibility is the limit switch for the blower is going bad or sticking.

dwesol

The new thermostat solved the problem. Thank you for your responses and suggestions!

redline