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Thread: Evohome replace existing dial thermostat

  1. #1
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    Default Evohome replace existing dial thermostat

    I think I have settled on evohome over heat genius - the one question I have is, can I replace my existing dial thermostat with evohome and set just set my heating to continuous or do I need to replace the controller on the boiler?

    I would happily replace the controller on the boiler, however it is a Stanley and also controls the oven...

    System is oil powered BTW as no gas here - hot water is on separate system and not part of this project

  2. #2
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    Set your heating to continuous. Either remove your old dial thermostat of turn it to maximum temperature, not needed anymore.

  3. #3
    Automated Home Legend paulockenden's Avatar
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    Or you could mount the Evohome controller there. The existing wires can be used for the power feed, just put the transformer in your airing cupboard )or wherever the other end of the wire is).

    P.

  4. #4
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    I don't want to high-jack this thread but I have related questions.

    I have a newly installed gas c.h. and direct hot water condensing boiler system. There is a Danfoss dial thermostat on the wall in the hall with a digital timer/controller on the wall next to the boiler housing unit.

    Changing the thermostatic valves seems straightforward enough. Do I simply remove the Danfoss wall thermostat and simply wire the ATP921R3100 into the 240 V supply only?

    How do I swop the BDR91 for the timer controller? Is it just the case of swopping a few wires from the timer/controller? There is no hot water tank so I just need to control the central heating.

    The BDR91 would then be located outside the boiler housing kitchen cabinet on the wall just about 200mm from the side of the boiler. Is this far enough away, considering the boiler housing cabinet is about 44mm thick?

    Other than ensuring a good wifi connection, is there any other particularly onerous technical installation procedure to consider?

  5. #5
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    Don't think that'll work.

    You'll need to remove the programmer and rewire to provide permanent live to thermostat location. This will power the Evohome controller, but because you've stolen what was a switched live for the thermostat the BDR91 will have to control the valve directly. You might have sufficient cabling to the programmer to do this (especially if the system used to do hot water through a tank or something) but in reality it'll be easier to have the BDR91 near the valve and just stick a blanking plate where the programmer used to be.

    Alternatively, you could replace the programmer with the BDR91 and then remove the existing thermostat, using the Evohome controller on it's stand and supplied mains adapter.

  6. #6
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    Thanks for your reply.

    Although I am fairly proficient in DIY, I am not very knowledgeable about your suggestions. I don't know what you mean by 'the valve' and controlling it directly.

    Our c.h. system is just a year old with a condensing boiler. There has never been a hot water tank. The h.w is direct and on demand.

    Can you elaborate on your explanation or direct me towards a manual or instructions?

    I don't want to purchase the system until I know I can fit it without any problems

  7. #7
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    Oh, right. If it's a combi boiler then there's no farting around with valves.

    You can remove the existing programmer and replace it with the BDR91, switching the boiler directly without going through the old thermostat. You're probably going to have to spend some time identifying some of the wiring behind your programmer, but it shouldn't be too difficult.

    You'll have a two or three core cable to the existing thermostat which you can appropriate to send 240v to the wall mount to power the controller.

    Wiring diagrams in the installation manual. You might also want to check if your boiler is OpenTherm compatible, as that'll make the heating more efficient and you won't need the BDR91.

  8. #8
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by Fursty Ferret View Post
    You'll have a two or three core cable to the existing thermostat which you can appropriate to send 240v to the wall mount to power the controller.
    I wouldn't do it like that. I'd mount the transformer at the 'junction box' end of the cable, and just send low voltage DC down the existing cable to the wall mount. That way you don't need a wall-box behind the controller (to house the transformer), you can just mount the plate flush on the wall.

    P.

  9. #9
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    True, but if there's an existing thermostat there's probably already a wall box fitted in a convenient bit of the house, and the wall mount bit comes with a dinky transformer that fits perfectly.

  10. #10
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    Thanks to you both for your further replies.

    The condensing boiler is a Viessmann Vitodens 100W. I note that Viessmann produce Open Therm compatible boilers, but I would have to check if my specific model comes into this category. Can you please explain how I can discard the BDR91 and how this would be more efficient? If it was possible to dispense with the BDR91 does this mean a more complicated installation procedure?

    The Danfoss wall thermostat in the hall is fitted to a plastic wall box so can I assume that this would be a straightforward installation by simply connecting to the existing 240V cable?

    If the BDR91 is utilised I assume it can be simply substituted for the controller with the appropriate wires swopped over, or is it more complex than this?

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