Question about Honeywell Programmable Thermostat Heater

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Honeywell CM921 Showing room temp at -24 degrees, How do I reset?

Thermostat is showing -24 degrees and heating system is burning. The actual room temp is approx +22 degrees so the sytem is not switching off. How do I reset or has the thermostat broken?

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  • d_corscadden Nov 12, 2008

    Thanks boanhtgclg,

    Contacted the manafacturer and they have confirmed a fault on the circuit board and have replaced it, But thanks for your suggestion

  • craigskel Jan 22, 2009

    I also have this problem. I have tried following the various tutorials to resync the thermostat to no avail.



    I've tried contacting the manufacturer but can't get through. Does anyone know if this is possible to fix?



    Any help would be greatly appreciated.



    Craig

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Honeywell cm921 problem with red light flashing tenp not controling boiler can any one hel

Posted on Dec 15, 2009

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Heya this is a manufacturing fault from honeywell them selves when it comes up -24 basically it needs to be replaced there is no way around in if you get in touch with honeywell they are generally good about it also if you provide them with the date code and model code they will be greatfull as it seems they have sent out a "bad batch". you locate this by:

A) Move the slide in to the off position
B) Press and hold i for 5 seconds
C) Unit will enter settings mode
D) Press and hold the i button and the + and ¿ button together
E) The unit will hold the relay on for 5 minutes and you can view by pressing the down arrow twice for model id/date code (ww/yy)

I hope this helps

Posted on Feb 12, 2009

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Go to the furnace and switch the power on/off so that it resets itself, get back to me

Posted on Nov 12, 2008

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HONEYWELL WEBSITE:
Go to honeywell.com
Under red welcome sign
Bottom red highlighted box literature/image search
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Click on arrow to right
Then click on the PDF files owners manual / installation instructions
If you can’t find what you want, the bottom left and bottom of web
Page, they have homeowners assistance and Home products to get the help you need.

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