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Thread: Evohome / Ideal Logic Boiler / Openterm

  1. #1
    Automated Home Lurker
    Join Date
    May 2017

    Default Evohome / Ideal Logic Boiler / Openterm

    Hi Guys,

    We have Evohome and DHW using 2 x BDR91 and the boiler is a Ideal Logic S24. We are looking at adding in openterm to the boiler and getting the evohome bridge , but our question is what happens when there is demand for both CH and DHW, does the flow temperature get increased while there is DHW demand ? Boiler is currently set to economy mode. And what happens when there is only demand for DHW like in summer time ? Any help would be great ,


  2. #2
    Automated Home Jr Member
    Join Date
    Sep 2018


    When there is a DHW demand, Evohome will issue a 100% request to the OpenTherm bridge. The bridge will map this to your boiler’s Max CH Setpoint water temperature. This is 90C with my Intergas boiler but is capped at the temperature set by the boiler’s controls e.g. 60C for CH. By default my boiler cannot distinguish between a CH and DHW request.

    To overcome this and avoid radiator overshoot I have a Priority DHW setup. Two BDR91s are bound to the stored hot water setup. One BDR91 opens the normally closed DHW two port valve and closes the normally open CH two port valve. The other BDR91 switches in the normally shorted cylinder NTC sensor resulting in the boiler switching to DHW mode and heating at 70C and 20kWh based on boiler parameters, quickly reheating the cylinder.

    While the cylinder is reheating there is no radiator flow but I do have a UFH zone controlled by an HM80 that can mix down the higher flow temperature.

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