Advice on converting a Honeywell CM707 thermostat to Drayton Wiser

21 Nov 2018
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United Kingdom
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 ( 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


  • CM707 wiring.jpg
    CM707 wiring.jpg
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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.
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
Did you manage to sort this out mate? I have a new build house. It has the cm907 connected to the boiler. Behind the cm907 there is a live, earth, neutral and a grey wire that has the end cut off and just tucked in. I have tried to wire it by putting a loop between live and pin 1 on the wiser. It has powered up but the green and red lights flash on the hub now. The heating has come on and the water working but nothing else works and won’t link to the app. Obviously words wrong. Can I not wire the Drayton up with these wires? Anyone know what the cut off wire will be? It’s grey in colour. It’s a Barratt house less than 8 years old. What does the flashing red and green lights mean?
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To be honest I noped out and got a Hive set-up with an engineer on quite a good deal. I quite like the Hive, and there's the option of having radiator thermistor down the line if I want it. The engineer managed to hook up everything really quickly, so I suspect if you know what you're doing it's easy. I just really can't advise you what all the wires do. Sorry!
That’s ok. The grey wire in mine is cut. I have have checked it at the boiler fused switch end. It is also cut in that. I am guessing that means the grey wire could simply be connected to a live feed in the fused switch area making it a live feed at the thermostat end and would therefore make it work though not quite sure about this so won’t attempt it without advice. Will look at the the one you have just in case this one needs to go back. Cheers.

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