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Thread: Evohome no HW zone valve

  1. #1
    Automated Home Lurker
    Join Date
    May 2021

    Default Evohome no HW zone valve

    Apologies for starting a new thread, but I have been reading numerous threads all week and i think i am more confused
    My parents home has been using a Rayburn 499K oil burner to control CH & HW for 20yrs and its on it last legs. There never was a thermostat on the HW cylinder.
    So I have got a Grant Vortex boiler installed to use primarily for CH & HW, with the rayburn still being used for cooking(and backup heating source).

    Talking to the plumber, he didnt want to add a zone valve to the HW, due to the complexity with the Rayburn still able to run.
    The new system has 1 zone valve, so when I press CH ON it heats CH and HW. Im ok with this.
    When i press HW ON, the boiler and pump runs which heats up the HW tank.
    I have tried to detail this a bit more in the attached schematic.
    I am unsure about the how HW ON is wired (red in schematic), until next time i can check junction box.

    Current Setup.jpg

    SO I was thinking of adding Evohome to control the new boiler - and keeping current programmer in parallel to Evohome as its easy to use by my elderly parents.
    I am thinking 2 bdr91's - 1 for Heating Zone valve, and other for boiler relay to control HW.

    Evohome Proposal 1.jpg

    I have 2 off HR91's which I was thinking of installing in living room and parents bedroom also.
    I want to get this all correct in my head before i get an installer involved.
    I am unsure if I have got the wiring correct. An help or suggestions would be welcomed.

    Thanks in advance.

  2. #2
    Automated Home Lurker
    Join Date
    May 2021


    i think i scared everyone off lol

  3. #3
    Automated Home Jr Member
    Join Date
    Jan 2019


    You wouldn’t wire it in parallel, it would be in series - ie the controller would only provide power to the BDR if it was set as on.

    The Rayburn would need an open loop so that the temp in the line would remain at an appropriate temp when it was running.

    TBH if you are thinking of installing EH it is really designed to control all the rads independently. For the CH, it should be set as permanently on at the controller (or wired through) with all rad valves fitted with a HR 91/92.

    Wiring in series would result in you only getting heat in the house when the HR92s called for heat.

    Wiring in parallel would result in the whole house getting heat when your existing thermostat called for heat but possibly not in the two rooms with HR92s depending on the room set point

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