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.
Vaillant 831 Ecotec Plus going over set temp
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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.
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Originally posted by Johntheo View PostIf 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.
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Originally posted by garymtitley View PostThink 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.
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Originally posted by Johntheo View PostYes, 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.
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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.
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Originally posted by bruce_miranda View PostAnd 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.
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Originally posted by garymtitley View PostSo 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.
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Originally posted by bruce_miranda View PostYes, 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.
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Originally posted by bruce_miranda View PostCorrect, a heating system, like life, is full of compromises.
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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