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Thread: Vitodens 111-W DHW Control

  1. #1
    Automated Home Lurker
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    Jan 2021
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    Default Vitodens 111-W DHW Control

    Good afternoon all,

    Apologies for going around the buoy again on an already discussed topic.

    I have a Viessmann Vitodens 111-W boiler, Honeywell Evohome with BDR91 relay and HR91 TRVs. I work away from home and currently the only control that I have over the DHW is to turn it off at the boiler whenever Iím away.

    I have the hot water kit but now have the issue that I think that I will need the OpenTherm Controller to be able to utilise this.

    My future intention is to use OpenTherm but would prefer to not have to shell out post Christmas, is there a way to control the DHW without? I have read through the thread regarding 111-W overshoot and seen a number of recommendations to return to BDR91 but canít see where on the electrical connections it could/should go.

    I will also be getting the OpenTherm Gateway to address the overshooting issue but again would prefer some time to raise funds.

    Thank you in advance.

    Tom

  2. #2
    Automated Home Legend
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    Jul 2014
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    Default

    If the Viessmann Vitodens 111-W boiler's HW can be controlled using an external programmer, then it can be controlled using a relay. So does it? If all you want is app control of that HW switch then just stick a Wemo or Alexa plug on it - job done.

  3. #3
    Automated Home Lurker
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    Jan 2021
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    Default Electrical Connections

    Unfortunately the only electrical connections in terms of control are through F connection (controlling CH and currently being initiated by BDR91) and the OpenTherm connection. I think that the Viessmann controllers use OpenTherm to monitor the DHW and maintain temperature/schedule. (Attached diagram).

    Iíve seen people on previous posts talk about reverting back to BDR91 as a result of OpenTherm overshoot so didnít know if there was a way of controlling DHW that I couldnít see. The DHW cylinder is powered by the same circuit as the rest of the boiler therefore no possibility of isolating it and using a controllable socket.
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