Original message
| amyhughes
 |  "furnace ignoring thermostat setpoint"
, posted Sun 2 Mar 19:09  
I've had the following problem for 15 years and finally bought a new thermostat, and it didn't solve the problem.
Frequently (multiple times per day) I'll feel hot, so I'll go to the thermostat and find that the setpoint is 72, the current temperature is 78, and the furnace is turning *on*. So I'll reduce the set point 2 degrees and eventually the furnace will stop, and an hour later I'll feel cold. I'll check the thermostat and find that the current temperature is 65, the set point is 70, and the furnace is off. So, I'll increase the set point two degrees, the furnace will turn on, and the cycle will repeat.
The new thermostat is a basic honeywell digital model. I use it in "run mode"--no timer, just a constant temperature. The old one is a late-80's vintage analog Trane. The furnace is a late-80's vintage Trane gas model, apartment size.
Any clue why this furnace does this?
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Replies:
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| dwcaveney
| "Clean your furnace" , posted Fri 7 Mar 03:01
Do you change the filter every 60 days? Are the ducts clean? How many wire are hooked up to your T-stat? Is the control board full of dust and dirt?
Turn off power, remove access panels, vacuum furnace, clean ducts, change filter.
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