Old wireless Honeywell CM927 thermostat

I’ve just bought a house, in which there is an old Honeywell CM927 thermostat controller. It’s not wired into the wall , I can carry it around. Two questions- how does it work. And how do I replace it? There are no other controls anywhere , just a standard combi boiler. The display on the CM927 is missing some letters so I think it’s on its last legs and I’m concerned that when it dies, I don’t know how to replace it without hiring a plumber. Any advice gratefully received! 

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  • Ref44
    Ref44 Posts: 68
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    Somewhere near the boiler will be a receiver unit with a cable running to the boiler. It may have some lights on it. The two units act as a pair; the receiver switches the heating on and off using the signal from the thermostat. A replacement would consist of the same two units.
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    edited 18 November 2023 at 9:57AM
    You can almost certainly buy just the 'stat part and re-pair it with the existing receiver, but they aren't cheap units either way.
    Are you interested in going 'Smart'? Ie, full programming control via your phone? Set your heating even when you are away? Even add Smart TRVs on some rads to control them individually. If so, check out Wiser, Nest, Hive and others.
    Sadly, the existing receiver doesn't appear to have a 'standard' backplate that could allow a clip-on replacement, but the wiring will, nonetheless, be straight-forward. If you can wire a plug, then...
    (We'll guide you.)
  • flo22
    flo22 Posts: 317
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    just because some letters have worn of does not mean it's on it's last legs, does it still work?
    30+ years working in banking
  • daveyjp
    daveyjp Posts: 12,373
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    As a start change the batteries in the wireless unit.  If its still not working you can buy a new unit and pair it with the unit on the boiler.
  • Jonboy_1984
    Jonboy_1984 Posts: 1,187
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    Ref44 said:
    Somewhere near the boiler will be a receiver unit with a cable running to the boiler. It may have some lights on it. The two units act as a pair; the receiver switches the heating on and off using the signal from the thermostat. A replacement would consist of the same two units.

    The honeywell receivers I have seen also have a single grey button used to put the receiver into sync mode for pairing a new controller to them. 

    There are various thermostats available at screwfix. 
  • FreeBear
    FreeBear Posts: 14,222
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    If you are going to the expense of replacing the thermostat, get a programmable one. This would give you the opportunity to set different temperatures throughout the day & week. Potentially, up to 10% saving on gas consumption.
    Her courage will change the world.

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  • Lorian
    Lorian Posts: 5,664
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    edited 19 November 2023 at 8:10AM
    The cm927 is a pretty good stat for an older model but does suffer from the display failing due to delamination. It can be repaired but involves disassembly, clamping the display and heating it. Not a fix for a novice. You'll find videos on eBay on how to do it but it doesn't always work.

    The cm927 is a 7 day programmable stat. It has 0.5c steps (better than nest for example) and has useful options to control overshoot, reduce short cycling and has good hysteresis, so whatever you replace it with its unlikely to save you any money.


  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    Yes, it's a decent device, when it works.
    I personally wouldn't buy another, tho', as it seems hugely overpriced. You can buy Smart for similar, or even less.
  • kev1744
    kev1744 Posts: 147
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    i had exact same issue with my cm927. if you search online for a pro wireless stat it is a direct swap for the cm927.i think it cost me about £50 took me about 5 minutes to swap them. no need to change the receiver just press a couple of buttons and that was it.
    having said that i would first swap the batteries in the cm927 just in case its the batteries that need changing.
  • I’ve just bought a house, in which there is an old Honeywell CM927 thermostat controller. It’s not wired into the wall , I can carry it around. Two questions- how does it work. And how do I replace it? There are no other controls anywhere , just a standard combi boiler. The display on the CM927 is missing some letters so I think it’s on its last legs and I’m concerned that when it dies, I don’t know how to replace it without hiring a plumber. Any advice gratefully received! 

    I have one of these - it's brilliant. I use it in combination with thermostatic radiator controls (and good insulation) to keep on top of my energy bills.
    It's programmable for the week, it judges temperature based on whatever room it is in so in the morning, for instance, you can have it in the bedroom and not use excessive energy heating a living room to full temperature. You can just hang it on a wall and use it like a 'normal' central heating control if you prefer. 
    I don't want lots of data-stealing 'smart' controls. I'm not a luddite, I can code. But these Honeywells give you the best of both worlds unless you really want to use your phone to control your central heating. 
    You can find the manual by Googling. 
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