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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7542
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a comfortSense 7500 thermostat. With a 4 month old

Customer Question

I have a comfortSense 7500 thermostat. With a 4 month old Lennox system. Last night we had the thermostat set to 71 and woke up the middle of the night freezing. The temp was down to 66 and we couldn't shut the unit off. Selecting off did no good as well as bumping the temp up to 78 on the thermostat. I finally unplugged the unit. Plugged it back in this morning. It shows OFF on the thermostat but the unit came back on and is blowing cold air. HELP!!
Submitted: 4 months ago.
Category: HVAC
Expert:  Phil replied 4 months ago.

Hello, that is either a defective thermostat or a defective printed circuit card, or a short in the thermostat wiring where it runs inside the wall and stapled to the studs.

Any work you do on it can be cause for the Lennox dealer to complain and deny part of your warranty...he owes you a fix.

If, none the less, you wish to attempt a repair yourself tell me a lot about your technical skills and if you have a multi meter and a few hours to spare,

We can go from here without a time limit.

When you have what you need from me, please locate the 'finish and rate your expert' link and click on it, that is the only way the company pays me for my time.

I will appreciate it.

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