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Thread: Evohome + Opentherm v Evohome + Boiler Outside Weather Compensation

  1. #51
    Automated Home Legend paulockenden's Avatar
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    'Conventional' S-Plan setup is 2 x BDR91s, one controls the HW valve, the other the CH valve. And then it's the output FROM THE VALVES that fire the boiler. There's no direct Evohome connection to the boiler. There is NO boiler relay.

    'Alternative' S-Plan setup (only if you have HR92s on all of your rads) is you lock the CH valve so that it is always open, and have one BRD91 for the HW (as above), and the other bound as a boiler relay.

    Does that helps?

    I'm assuming that for Opentherm you start from this 'alternative' setup, and replace the boiler relay with the OT Bridge.
    Last edited by paulockenden; 4th April 2016 at 12:00 PM. Reason: typo

  2. #52
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    So in the "Conventional" S-Plan setup. How do you bind the BDR91 for the CH valve?

  3. #53
    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by bruce_miranda View Post
    I understand the HW and the UFH zone valve wiring and BDR91 binding because that is very simple. It both cases the BDR91 is bound as the actuator which in turn opens the relevant zone valve. The Opentherm bridge will now independently fire up the Boiler because it too knows there is heating demand.

    What I don't understand yet is the CH zone valve wiring and BDR91 binding. I thought that the whole point of a "System Device Boiler Relay" was so that if any radiator or HW needs heat it would trigger the boiler relay.

    Now if I replace the boiler relay with the Opentherm, the Boiler Demand is handled by the Opentherm, so the boiler will start up. But how will the CH zone valve open when there is CH demand? How do I bind the CH zone valve BDR91? I can't bind it as a Boiler Demand System Device because that is now the Opentherm bridge. So what options to I use to make sure that the CH zone valve opens whenever any of the TRV zones need heat.
    the S Plan heating valve BDR91 is bound during guided configuration on the hot water path
    the CH zone vale than automatically opens whenever there is a heat zone demand

    have you taken the www.youlearn.honeywell.uk.com online training, this should help your understanding
    I work for Resideo, posts are personal and my own views.

  4. #54
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    Yes I have been through the online training.

    Like I said I understand the HW part fine. It's the CH part that I don't understand.

    How is the CH BDR91 bound to the evohome in a normal S plan? Is it bound via the System Devices Boiler Demand Boiler Relay or some other way?

  5. #55
    Automated Home Legend top brake's Avatar
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    Quote Originally Posted by bruce_miranda View Post
    Yes I have been through the online training.

    Like I said I understand the HW part fine. It's the CH part that I don't understand.

    How is the CH BDR91 bound to the evohome in a normal S plan? Is it bound via the System Devices Boiler Demand Boiler Relay or some other way?
    the S Plan heating valve BDR91 is bound during guided configuration on the hot water path
    the CH zone vale than automatically opens whenever there is a heat zone demand
    I work for Resideo, posts are personal and my own views.

  6. #56
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    I re-looked at the training demos again. I think that when you use the radiator TRV valves you are not supposed to use a CH zone valve as well but instead control the boiler directly via the Boiler demand. And if you have a CH zone valve you need to have it open all the time.

    115438_4xGraphics5.jpg

    The only time you would have both HW and CH zone valves is only if you had only 2 zones i.e. HW and CH (whole house). i.e. a bog standard S Plan (or Y plan).

    115438_4xGraphics2.jpg

    Ok back to the Opentherm question then. Will the Opentherm bridge operate the Boiler for any demand? Be it Hot Water, Radiator or (in my case) the UFH zone valve? The reason I ask is because I will now fully relying on the Opentherm to start the boiler. The BDR91s will only be operating the motorised zone valves, which will have their Orange wires disconnected from the boiler.
    Last edited by bruce_miranda; 4th April 2016 at 02:12 PM.

  7. #57
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    Quote Originally Posted by bruce_miranda View Post
    So in the "Conventional" S-Plan setup. How do you bind the BDR91 for the CH valve?
    Read the advice at The Evohome Shop - Help. I have a 2 valve system with 2 BDR91s. All radiators have HR92s. CH is turned on by a Zone calling for heat which, in turn, activates the BDR91 to open the CH zone valve. Knowing very little about CH, I consider the BDR91 to work in the same way as my old Hall thermostat. It clicks, the zone valve opens and the boiler comes on.

    The confusion - as explained by Richard - is Honeywell's choice of terminology. The BDR91 that controls the CH has to be configured in the controller as a Boiler Relay.

    The alternative is to leave the CH zone valve open and the use the BDR91 to control the boiler whenever a zone demands heat.

  8. #58
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by HenGus View Post
    The BDR91 that controls the CH has to be configured in the controller as a Boiler Relay.
    I think that's wrong.

    In the setup you've described ("CH is turned on by a Zone calling for heat which, in turn, activates the BDR91 to open the CH zone valve") it's important that the CH BDR91 *isn't* configured as a boiler relay. (In an S-Plan setup).
    Last edited by paulockenden; 4th April 2016 at 02:44 PM. Reason: Clarity

  9. #59
    Automated Home Legend paulockenden's Avatar
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    I think I've got these right:

    evo-s-conventional.jpg

    evo-s-alternative.jpg

    (I've never seen an official version of the second one).

    Note that in the alternative version the boiler is controlled by the boiler relay, not the valve outputs.

    P.
    Last edited by paulockenden; 4th April 2016 at 03:19 PM.

  10. #60
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    Quote Originally Posted by paulockenden View Post
    I think that's wrong.

    In the setup you've described ("CH is turned on by a Zone calling for heat which, in turn, activates the BDR91 to open the CH zone valve") it's important that the CH BDR91 *isn't* configured as a boiler relay. (In an S-Plan setup).
    Now - I am confused. when I changed the controller I just copied what my Honeywell Specialist Installer did when he set up the system, and when he replaced the controller a year ago. If I look in System Devices - it shows that the Boiler is controlled via a 'Wireless Relay Box'. When heating is demanded, I can hear the Zone valve open followed by the boiler coming on. When heating is no longer need, the BDR clicks and the zone valve closes. My system has been working like this now for nearly two years. Am I missing something?

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