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Thread: X-Plan

  1. #11
    Automated Home Guru
    Join Date
    Sep 2018


    Quote Originally Posted by lloyd View Post
    Ok so this is where my complete lack of knowledge of OpenTherm (and perhaps naivety about evohome) shows. I had assumed, probably wrongly, that if you were using OT with evohome, then evohome would boost the max flow temperature if DHW was being call for.
    Ideally Evohome would allow you to set different max CH and DHW OpenTherm temperatures, but unfortunately it doesn’t. And with some boilers the default 80C or 90C is too high.

  2. #12
    Automated Home Sr Member
    Join Date
    Mar 2016


    I use this x-plan setup. My heat-only viessman boiler will not produce the high flow temps needed to heat a DHW cylinder unless its "DHW demand" terminal has voltage applied. without that , the flow temp is in the 50's.
    So, the evohome HW BDR is wired to open the DHW zone valve. The end-terminal of the DHW zone valve is wired to close the (normally open) CH zone valve and activate the DHW demand mode on the boiler giving 79C flow. Result = 79C water going only to the cylinder. downside is heating circuit has no flow for the reheat time so timing is key.

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