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Honeywell Thermostat won't turn on

It was working just fine yesterday afternoon. But last night we noticed it felt warmer and when I went to turn it down, there was nothing on the display. We've checked the fuse box; nothing was tripped. We've popped the unit off the wall and put it back in - nothing. Ideas?

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  • melmoore Aug 05, 2008

    Not that I know of, but then I'm really bad with electronics and repair. The model is a T8411R102 if that helps.

  • Anonymous Sep 21, 2008

    Thermastat will not turn on. Was working fine and I went to turn temp down and it was off. No directions on how to trouble shoot.

    [email protected]

    SHARCNET-USA May 11, 2010

    Is there an internal battery? My Honeywell has one.



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There is a small automotive type of fuse in your air handler (not thermostat), check that. Also check to see if the Emergency Switch somehow got turned off (Usually found in stairwell or closet).

Posted on Aug 07, 2008

  • RobbiDobbi Aug 13, 2011

    5 amp fuse in air handler was blown. Replaced and working fine. Thank You.


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Check the water sensor in your drain piping if you have one. If it's sensing water backing up, it will blank that display.

Posted on Oct 06, 2009

  • B Frank Stokes Jr Sep 07, 2011

    Thanks to furcifer, that solved my problem. With that water sensor sensing water in the pipe, it shuts everything down. Thanks again.

    Frank S

  • Anonymous Sep 09, 2011

    Glad it helped somebody!


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I have the same problem... after a thunder storm and the electric company shut off all the electricity in in my area but when the eectricity went back my thermostat is off.. no display.. i tried changing it still the same.. the electric company came and checked if theres a problem with the power supply.. they said theres nothing wrong.. not they told me to call the air conditioning guys to have my unit check... i dont know what to do.. should i call them?

Posted on Jun 09, 2010

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It could need the 3 batteries replaced. I just did that and now it will come on but won't light up. Trying to solve that now.

Posted on Mar 22, 2010

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