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Thread: Honeywell evohome and Vaillant ecotec plus 838

  1. #21
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    Let us know which online place too.
    Anyway, don't assume you can replace the room stat with the bdr91 because there are various room stats and only if your room stat is a full 230V 4 wire, with permanent live, can it directly replace the bdr91. Most aren't. Also the bdr91 also shouldn't have its live supply cut, which might be the case with the room stat. So I would leave the wiring to a trained electrician. Best to get the bdr91 and the boiler running off the same switch. Infact the ideal location for the bdr91 is crucial if you want to avoid transmission errors. So it also depends where your evohome controller is.

  2. #22
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    If your old timer is separate from the boiler it's usually best to install the BDR91 in place of the timer, and remove/bypass the wall stat completely at the wiring centre end. That's what I did.

    It also depends on whether your boiler control needs switched 240v or voltage free relay contacts - the BDR91 can do either but you have to be careful to wire it the correct way for your boiler.

    Personally I would not fit the BDR91 in place of your wall stat in the hallway, I would put it either in place of the timer or if that is not near the boiler install the BDR91 near the boiler.

    If you're unsure about the wiring it's possibly best to get someone in to do that part of the job for you.
    Last edited by DBMandrake; 5th November 2016 at 02:31 PM.

  3. #23
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    Most combis have the timer built into the boiler.

    If not, then Simon's suggested method is exactly what I did. Infact I ran my old dual channel timer and the two zone bdr91s in parallel while I worked out how to get Opentherm to automatically trigger my boiler.
    Last edited by bruce_miranda; 5th November 2016 at 02:40 PM.

  4. #24
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    So as bruce_miranda says the timer is built into the boiler. We open the front flap of the boiler and there is an analog timer there which we use to depress on the timer clock the times we want the heating to be on. So with that, where would the BDR91 go? I'm definitely not planning to do the install myself because I figured out a while ago that it was beyond my abilities! I've got a sparky coming next Saturday so he'll do it but I just want to be clear on the install myself as well.

  5. #25
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    Any thoughts anyone?

  6. #26
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    Quote Originally Posted by freddyq View Post
    Any thoughts anyone?
    If the timer is built in I would have the BDR91 installed near the boiler (but no closer than 300mm as per Honeywell's guidance of placement of RF devices) and wired back to the boiler in place of the old room thermostat. Then you put the boiler on constant. The wires to the old thermostat should be disconnected so they are not live.

    Remember you don't have to see or get to the BDR91 during normal use - the button is only for initial set up and as a temporary override when testing, you don't use it in day to day use. And the light is only useful if you want to know when the boiler is running, but you can probably see that directly on the boiler as well.

    If you later wanted to get a wall mount for the evotouch controller and install that where your thermostat used to be, the wires to the old thermostat location could be re-purposed for power to run the evotouch, as long as they were mains rated wires - this is what I did. An electrician would be able to do this easily.

    Where is your boiler located in the house ?
    Last edited by DBMandrake; 7th November 2016 at 08:59 AM.

  7. #27
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    Just remember that boilers are big metal boxes, not something you want close to an RF device. Let the electrician handle this...

  8. #28
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    Quote Originally Posted by bruce_miranda View Post
    Just remember that boilers are big metal boxes, not something you want close to an RF device. Let the electrician handle this...
    Most electricians don't know much if anything about RF signals and propagation so left to their own devices they would probably want to install the BDR91 right beside the boiler, hence why I pointed out no closer than 300mm.

    It does say it in the Honeywell installation booklets but who reads those!

  9. #29
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    Thanks @DBMandrake. So just to understand it in layman terms, the current basic wired thermostat we have installed on the wall in the hallway will obviously have wiring going to the boiler. So what you're saying is that the BDR91 should be wired to the boiler in place of the wires coming from the thermostat? If so, how will it get power? I'm aware of the 30cm rule as I've seen that in the installation guide so that's fine - the boiler is in the kitchen but enclosed by a tall unit so that it is hidden away and blends in with the kitchen. There should be enough space in that unit to keep the BDR91 more than 30cm away.

  10. #30
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    The BDR91 will need permanent live power yes, and as I mentioned earlier exactly how you wire it will depend on whether the boiler control input of your boiler that used to go to the wall stat is expecting switched 240v live or whether it just has two low voltage contacts that must be connected together by a switch or relay.

    If it expects switched live then you only need 3 wires to the BDR91 - permanent live, neutral and the return switched live that goes to the boiler control input. You connect a link wire across the back of the BDR91. If the boiler uses low voltage contacts on the other hand you'll need 4 wires - Permanent Live and Neutral to power the BDR91 only, then two additional wires from the relay in the BDR91 to the thermostat input on the boiler. (No link wire on the back of the BDR91)

    Both of these wiring scenarios are shown in the diagrams that come with a BDR91 and in fact some BDR91's come with the wiring diagrams on a sticker on the front.

    Your electrician would need to check your boiler manual to see if your boiler expects switched live 240v or has low voltage control inputs that expect only a switch. If you feed 240v into a control input not expecting it the boiler could be damaged.

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