Vaillant 831 Ecotec Plus going over set temp

[Johntheo]

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.

[garymtitley]

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.

[bruce_miranda]

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.

[garymtitley]

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.

[bruce_miranda]

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.

[Johntheo]

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.

[bruce_miranda]

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

[Johntheo]

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.