Question about Honeywell Programmable Thermostat Heater

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We've programmed our Honeywell CM927 to come on at specific temperatures at set times, but at certain times it comes on at very different temperatures. For example, at 11pm we set it for 16 degrees overnight, but last night it was running all night and had set itself at 22 degrees. We have checked the program for every single day of the week, and 11pm is set for 16 degrees all 7 days. It does the same thing in the afternoon - set for 18 degrees, it comes on at 22. We watched it and the 18 we set it at briefly appears in the display, but is replaced by 22 immediately. Ideas?

Posted by Mike Gerrard on


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Chris Harvey

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Most programeres have a factory preset time, you will have to find them and reset them to your own requirements

Posted on Oct 20, 2011

  • 3 more comments 
  • Mike Gerrard Oct 20, 2011

    Thanks, Chris, but it's not set on the factory settings any more.

  • Chris Harvey
    Chris Harvey Oct 21, 2011

    type honeywell cm927 problems in google search and you will find cm927 user guide. one of the things it says is there are 6 preset tines daily, and how to reset them.if you reset it sucsessfuly and you still have problems,sugest changeing prograner, or have it checked out.

  • Mike Gerrard Oct 21, 2011

    Thanks for your help, Chris. I have been emailing Honeywell's helpline via their website and they have been very good. It seems the culprit may be a feature called Optimum Start, which switches the system on early to the next pre-set temperature in order to get it up to temperature by the time it's supposed to come on.

    Yesterday afternoon it came on at 4pm at the temperature we'd set for 6pm, so we're guessing that's the cause. Honeywell told me to try disabling the feature to see what happened, but so far they haven't told me how you disable it! There is one paragraph in the manual describing how the feature works, but nowhere does it say (not even in the installation manual) whether you can disable it.

  • Chris Harvey
    Chris Harvey Oct 21, 2011

    hi mike i notice in the manual it says optimum start is set by the instaler so from that i presume that they should know how to disable it

  • Mike Gerrard Oct 21, 2011

    Yes, they have now told me how to disable it (and alter other factory settings) so we're giving that a try.



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