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atgrassi · Jan 19, 2009, 08:29 AM

I have a Lennox G32-75 gas furnace and a Honeywell T8401C thermostat.

I have been setting the thermostat temperature at 69 and the furnace continues to heat the house higher than the preset (up to 77-80 degrees). I am having to shut the thermostat off (which does shut off the furnace) and then bring the temperature back down to 69 (or below) before I turn the thermostat back on for heat.

I have been having this problem for the last month, however when I had the thermostat off for a few hours and then started back up, the temperature would stay at 69 for a few days and then all of a sudden, start to go up again. Just in the past couple of days, this has not been working... I turn the thermostat back on at 69 and then after about 30 minutes, it starts heating the house back up over 69.

I have noticed that when the house is heating up over preset temperature of 69 (say 71) the furnace does shut off for a time, but then turns back on at 71 and heats the house more.

Before I call a technician, I want to make sure that #1) it's something that I can't fix myself and #2) If I can't fix it myself, understand what the problem is so I don't get railroaded.

Thanks in advance for your help!

dac122 · Jan 19, 2009, 10:24 AM

The first thing I'd suspect is the thermostat as shutting it off appears to clear the problem temporarily. If you know how to use a multimeter I'd be checking what's energized on the thermostat the next time it acts up.

hvac1000 · Jan 19, 2009, 10:25 AM

More than likely the problem is with your thermostat. It could be some sort of adjustment but it could also be that you need a new one.

On the other hand the start and stop of heating you mentioned if not being caused by the thermostat could also be the signs of a furnace problem.

It is almost impossible to tell from your description what is going on but I would bet it is the thermostat.