The temp increases when the boilers running,still demanding heat to satisfy what the Hr92 are asking for but instead of it staying at what’s been set at the boiler it continues to heat up between 5-8 degrees and then goes into anti-cycling mode until things cool again,then it will fire and run again.
Agreed, but my reason(s) are still valid, the minimum output of your boiler is 9kw, quite high, and its quite probable that your heating demand is less than this very frequently so flow temp increases to SP+5/8C, burner cuts out etc. If the heating demand increases do you see the flow temp returning to its setpoint?Originally Posted by garymtitley
Yes it totally understand what you are saying and that's probably right,unfortunately the boiler doesn't modulate to a low output,the flow temp does go down but only after it's shut down and goes into anti-cycle mode obviously with pump overrun.Its more than likely that the boiler is too big,going to replace it with either a Intergas or possibly Veissmann when it's due for replacement,the 831 is twelve years old now so it's not going to be too long.
Think you can get a Viessmann vitodens 200?? that will modulate right down to something like 1.9kw and is still capable of something like 36kw max output.
Well it seems I’ve had a bit of a breakthrough,over the weekend I’ve spent time carefully re-balancing the radiators and altering the range rating on my boiler and tweeking the flow temperature,it looks like it’s payed off,the boiler is still slightly going over the set temperature but not by as much,the result is that I’m getting long burns and a low return temperature,between mid 40s to low 50s with the outside temperature being close to 0 degrees which means it’s condensing most of the time.I’m much happier now and all the target temperatures are being met in all rooms which two were struggling before,will keep a close eye on this but it’s looking good,phew!!
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.
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.
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.
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