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Advice on converting a Honeywell CM707 thermostat to Drayton Wiser

Discussion in 'Plumbing and Central Heating' started by masterofninja, 21 Nov 2018.

  1. masterofninja

    masterofninja

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    Dear all

    Novice to plumbing and electrics. Interested in getting a smart heating system for my flat, and after considering Hive, Nest and Tado, narrowed my choices down to Drayton Wiser or Honeywell Evohome.

    I was going to go for the Drayton Wiser, and was planning how to install it. My flat is relatively new (last 10 years) and has a Honeywell CM707 thermostat (wired) connected to a Ideal Combo 35 boiler. The thermostat is out in the hallway away from the boiler.

    I was reading the Drayton Wiser install guide (https://www.draytoncontrols.co.uk/sites/default/files/WEB 15-03-18 8987 Wiser Instructions ISSH.pdf) and the options were to use an industry standard backplate.

    I took off my thermostat to see the wiring as the attached photo.

    My questions to everyone are:
    (1) What am I seeing here? Doesn't look anything like the wiring diagrams, so assume it's a Honeywell specific thing.
    (2) This backplate has only two wires - how would I wire up the "industry standard backplate"?
    (3) Should I cut my losses and get someone with experience to fit this?
    (4) Any advantages to using an OpenTherm interface as suggested in the Drayton manual?

    With Thanks
     

    Attached Files:

  2. stem

    stem

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    The industry standard back plate is generally associated with programmers. Some thermostats also use it but not all, the CM707 doesn't, it is so simple it only needs two wires connecting and doesn't need the 6 terminals the standard back plate provides.

    So, what you have posted is typical of a room thermostat. It is basically a switch that turns the heating 'on' and 'off' your two switching wires would have been connected to terminals A & B.

    The Wiser will come with its own back plate, so it isn't a problem.

    The problem you do have though is that the CM707 is battery powered, but the Drayton Wiser is mains powered, so as well as the two switching wires, the Wiser also needs a 230V supply to power it. This mains supply should come from the same 3A supply as the boiler, so if sufficient wires aren't present, a new cable will have to be run.

    If you have the possibility for Open Therm on your boiler it gives enhanced control and will adjust the boiler temperature as well as turning the heating on and off. However, AFAIK your boiler doesn't have Open Therm capability.
     
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  3. masterofninja

    masterofninja

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    Thank you very much for your reply!

    The website for these products make it sound so easy to install - obvious if you have a backplate thermostat, which from your reply I suspect most people don't have as standard. I'll need to get a plumber/electrician to fit this then.

    The boiler does have an option for Open Therm with an additional harness, which I'll see if I can get fitted.

    Thanks again
     
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