Vaillant 831 Ecotec Plus going over set temp

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  • garymtitley
    Automated Home Sr Member
    • Feb 2019
    • 59

    #16
    Just a bit of an update to my last post,I've just had my boiler serviced and checked,the engineer couldn't find any problems with the boiler but I'd ordered two new Ntc's,one for flow and one for return which I got him to fit whilst the boiler was being done,happy to say it's running much better and doesn't seem to be overshooting the set temp so all seems to be good,so it seems that atleast one of them was faulty.

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    • Johntheo
      Automated Home Jr Member
      • Oct 2021
      • 28

      #17
      So, if not overshooting the set temp then running continuously, or at least longer before cut out??.

      Comment

      • garymtitley
        Automated Home Sr Member
        • Feb 2019
        • 59

        #18
        Originally posted by Johntheo View Post
        So, if not overshooting the set temp then running continuously, or at least longer before cut out??.
        Yes it seems to be and maintaining a lower return temp until the heating demand is satisfied.

        Comment

        • Johntheo
          Automated Home Jr Member
          • Oct 2021
          • 28

          #19
          If I'm interpreting how Evohome works then even if the heating demand is > the minimum boiler output, it will keep cycling the boiler if all the rooms are within one deg of their setpoints?, it would be nice if it could summate all the HR92s % demands and if this sum is greater than a SP that could be user set then the boiler would fire continuously with higher efficiency and just as tight room temperature control?, maybe it does do this anyway by some other means.

          Comment

          • garymtitley
            Automated Home Sr Member
            • Feb 2019
            • 59

            #20
            Originally posted by Johntheo View Post
            If I'm interpreting how Evohome works then even if the heating demand is > the minimum boiler output, it will keep cycling the boiler if all the rooms are within one deg of their setpoints?, it would be nice if it could summate all the HR92s % demands and if this sum is greater than a SP that could be user set then the boiler would fire continuously with higher efficiency and just as tight room temperature control?, maybe it does do this anyway by some other means.
            Think your absolutely right and unfortunately with my boiler being too big and poor modulation turndown,that is the result,cycling.Now I am armed with much more knowledge,when I’m due a replacement I know what I need and I will probably go with a Veissman boiler and the guy who services has fitted them,he’s going to go on one of their courses and become a certified installer,that way I’ll be able to get the best warranty on it.

            Comment

            • Johntheo
              Automated Home Jr Member
              • Oct 2021
              • 28

              #21
              Originally posted by garymtitley View Post
              Think your absolutely right and unfortunately with my boiler being too big and poor modulation turndown,that is the result,cycling.Now I am armed with much more knowledge,when I’m due a replacement I know what I need and I will probably go with a Veissman boiler and the guy who services has fitted them,he’s going to go on one of their courses and become a certified installer,that way I’ll be able to get the best warranty on it.
              Yes, but even if you have a boiler with a very low minimum output, my understanding/query? is that the Evohome will still cycle it when all room temperatures are satisfied even when the boiler would be perfectly happy to continue firing.

              Comment

              • garymtitley
                Automated Home Sr Member
                • Feb 2019
                • 59

                #22
                Originally posted by Johntheo View Post
                Yes, but even if you have a boiler with a very low minimum output, my understanding/query? is that the Evohome will still cycle it when all room temperatures are satisfied even when the boiler would be perfectly happy to continue firing.
                Totally agree,think what you’ve said sums it up perfectly.Regardless of boiler output the boiler can do nothing but cycle once the target temperature has been met with Evohome.

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                • bruce_miranda
                  Automated Home Legend
                  • Jul 2014
                  • 2307

                  #23
                  And this causes all sorts of fun between you and your heating engineer, who is still using whole house heat loss calculations but in an Evohome system, you are almost never heating the whole house. And that is why the pursuit of a boiler with the lowest heat output, rather than the big old boilers. I have a 38Kw boiler, which thankfully has been derated at the top end to 18Kw, but I wish I could drop the floor.

                  Comment

                  • garymtitley
                    Automated Home Sr Member
                    • Feb 2019
                    • 59

                    #24
                    Originally posted by bruce_miranda View Post
                    And this causes all sorts of fun between you and your heating engineer, who is still using whole house heat loss calculations but in an Evohome system, you are almost never heating the whole house. And that is why the pursuit of a boiler with the lowest heat output, rather than the big old boilers. I have a 38Kw boiler, which thankfully has been derated at the top end to 18Kw, but I wish I could drop the floor.
                    So what you are saying basically is that the best thing is to install a boiler that has the lowest kw rating,for example a. Viessmann that can modulate down to 3.2 kw from say 24kw max.

                    Comment

                    • bruce_miranda
                      Automated Home Legend
                      • Jul 2014
                      • 2307

                      #25
                      Originally posted by garymtitley View Post
                      So what you are saying basically is that the best thing is to install a boiler that has the lowest kw rating,for example a. Viessmann that can modulate down to 3.2 kw from say 24kw max.
                      Yes, the lower the floor the better. You are probably never going to need the boiler at full pelt with Evohome. OT does help, a bit because it alters the flow temperature required as well.

                      Comment

                      • Johntheo
                        Automated Home Jr Member
                        • Oct 2021
                        • 28

                        #26
                        Originally posted by bruce_miranda View Post
                        Yes, the lower the floor the better. You are probably never going to need the boiler at full pelt with Evohome. OT does help, a bit because it alters the flow temperature required as well.
                        But, once the target temps are all met then Evohome will still cycle the boiler even though the minimum heating demand may be well above the boiler minimum output.

                        Comment

                        • bruce_miranda
                          Automated Home Legend
                          • Jul 2014
                          • 2307

                          #27
                          Correct, a heating system, like life, is full of compromises.

                          Comment

                          • Johntheo
                            Automated Home Jr Member
                            • Oct 2021
                            • 28

                            #28
                            Originally posted by bruce_miranda View Post
                            Correct, a heating system, like life, is full of compromises.
                            Yes, of course.

                            If I had Evohome installed and had a spare HR92 laying around I would set it very high to get the boiler to fire continuously (assuming prolonged heating demand > boiler min output) it would be interesting to see (if this works) what effect this has on room temperature control, etc.

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