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Thread: Honeywell evohome and Vaillant ecotec plus 838

  1. #11
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    Yes sorry I have a combi boiler and I actually read another post on here from someone who had the same boiler but lower power who had checked up and confirmed from Vaillant that the boiler itself has an embedded diverter valve with bypass.

    I've known all along I don't need the HW kit because that's all on-demand for us with the combi.

    So the towel rails don't have any controls on them as far as I know, they always heat up when the heating is turned on. The radiator in the hallway does have a manual thermostat so can be turned on an off so I would ensure that is in the on position.

    I'm just curious to understand if I have to have an ABV fitted now...

  2. #12
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    Currently how is heating controlled? Is it via a timer, room stat or both? You need to work out with evohome how will heat demand be requested for all radiators.

    My towel rails also dont have trvs but they get heated whenever any of the other radiators in the house demand heat. And i'm fine with that. But you may not be

  3. #13
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    We have an analog timer on the boiler which we use. There is a very basic thermostat on the wall in the hallway but we don't use that. I deliberately kept everything basic because I always planned to install a smart system. So I'm guessing with evohome I will switch the boiler from timer to on and then let the evohome control boiler on off times.

    And yea, I'm fine with the towel rails and hallway radiator being heated whenever any of the controlled radiators requests heat.

  4. #14
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    Then its a very simple installation. Just turn the timer clock to constantly on and replace the input of the room stat to the boiler with the bdr91, setup as the default boiler relay.

  5. #15
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    Wait so the boiler has three positions; on, off and timer. I thought I'd be leaving it to the on position with evohome but I actually need to leave it on the timer position but set all times to be on?
    "replace the input of the room stat" as in replace the basic dial thermostat in the hallway with the BDR91?

    It has also been suggested to me that I get the BDR91 wired between the power supply switch for my boiler and the boiler itself, set all timer times to be on. So the relay controls the power from the switch to boiler and it will only turn on when relay tells it to....?

  6. #16
    Automated Home Legend paulockenden's Avatar
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    If you do that you won't get any over-run, which will decrease the lifespan of your boiler.

    The boiler might also have a 'power on' sequence (effectively the controller booting up) which you'd be running every few minutes!

  7. #17
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    NO definitely dont cut the power to the boiler EVER! Boilers shouldn't be powered on and off. You should be controlling the flame trigger and that is normally done by the room stat. So now replace the room stat with the bdr91.

    Set the timer to ON and control the heating schedule using evohome.

  8. #18
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by freddyq View Post
    It has also been suggested to me that I get the BDR91 wired between the power supply switch for my boiler and the boiler itself
    Just out of interest, who told you that?

  9. #19
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    If you cut power to your boiler when you dont need CH, how will you get HW on demand? Combi boilers should never be switched of. So please don't get the electrician to install your evohome, if he suggested something as daft as that.

  10. #20
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    Of course, that makes a lot of sense. Maybe I misunderstood what was being suggested...either way I'm definitely not doing that. The BDR91 will have to go where the thermostat in the hallway is. It's a wired thermostat so I guess the BDR91 would be powered by the c wire.

    It wasn't actually the electrician who suggested it, was an online place.

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