Which Combi boiler works best with Evohome?

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  • G4RHL
    Automated Home Legend
    • Jan 2015
    • 1580

    #31
    Originally posted by filbert View Post
    Unfortuately, I'm not sure how to check the return temp. Domoticz, via the OTB, lists it as a parameter but it's constantly showing 71.7 deg. I do have a digital thermometer, so I'll play with that come the autumn.



    Thanks but the manual for mine says that Eco mode will learn patterns and won't keep heat exchanger warm overnight, for example. Hopefully, it's telling the truth! Not that I'd hear the boiler - it's so quiet and it's tucked away. I don't even hear it fire up when I'm in the next room.
    Mine did not seem to learn and I found little or no difference when I switched Eco mode off, other than I suppose less gas consumed. I had it on for about 5 days after installation and could hear it firing up in the early hours. I thought there had been a call for heat when there should not have been until realising it was Eco mode. Off it went. I see very little point in having Eco mode as surely the most economical mode is “Off”?

    It is a shame the boiler does not display the return temperature but I can guess it is low when I see the boiler has dropped the flow temperature to 34c! It will start off at the set 70c but once the house or zone is up to temperature the Evohome system and Opentherm regulate it downward to what is needed. That is my understanding but I stand to be corrected on that!

    Best advice as always is, set up your schedules, desired flow temperature. DMW temperature, CH boiler output (the lowest you can set it to) and forget it all. I had to learn many years ago to stop playing. During the summer I don’t switch off the CH but drop the set temperatures in zones to 18 or 19 but usually the natural temperature is above that because of the summer conditions.

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    • Johntheo
      Automated Home Jr Member
      • Oct 2021
      • 28

      #32
      Its the boiler return temperature that determines the boiler efficiency and has to be down to ~ 55C before any condensing effect, 55C gives ~ 86%, 48C gives 90%, 40C gives 95% & 25c ~ 98.5% so if the boiler flow temperature actually is 70C then very little condensing benefit if the dT is 20C but if its down to 35C for whatever reason then a big increase in the condensing benefit.

      Condensing Temperatures.jpg

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      • G4RHL
        Automated Home Legend
        • Jan 2015
        • 1580

        #33
        Originally posted by Johntheo View Post
        Its the boiler return temperature that determines the boiler efficiency and has to be down to ~ 55C before any condensing effect, 55C gives ~ 86%, 48C gives 90%, 40C gives 95% & 25c ~ 98.5% so if the boiler flow temperature actually is 70C then very little condensing benefit if the dT is 20C but if its down to 35C for whatever reason then a big increase in the condensing benefit.

        [ATTACH=CONFIG]1939[/ATTACH]
        Thanks. I am running at 70C with a 99% efficiency. Whilst the setting is 70C max it often drops down to below 40C for the flow temperature.

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