I have a 3 zone sealed heating system which comprises of an upstairs, downstairs and hw zones. The u/s zone has 11 rads and the d/s has 13 rads. The HW zone has a Megaflo indirect 250l cylinder, and until recently had a 1.3KW radiator attached too (more info on this below). The main pump is a Grundfos UPS 26-50r, upgraded from a 15/60 to try to improve flow. The d/s zone also has an additional 15/60 pump. The boiler is a Vaillant 438 and has been range rated to 26KW.
The d/s zone seems to work absolutely fine since adding the second pump (previously had problems with radiators not warming up). It heats up nicely within 20 mins either independently, or with the other zones open too.
The problems I have are as follows:
1) The HW zone when calling for heat on it's own works for a long period of time, but eventually starts short cycling to get fully up to the stat temp. I suspect this problem is due to my removing the additional radiator on the HW zone, which was recently done. I intend to add it back in. My question is, given the power requirement for all three zones, is there a solution to range rate dynamically when only the HW zone is calling for heat ? I understand a VR65 can independently control the HW flow temperature, but can it also control the output power to lower it ? Eg. If I range rate the boiler to 18KW, then the short cycling disappears. Am I right in saying the extra radiator should also alleviate this problem once again ?
2) The u/s zone seems to have a flow problem. If I have only the u/s zone calling for heat, I can see the flow / return delta is quite large. The return temperature seems to take an absolute age to increase. This frequently causes an S53. What else can I do to try and resolve this - would a second pump on the u/s circuit help ? Do I need a larger pump than the 26-50 ? What's strange to me is that all of my d/s radiators drop from u/s, so the "index circuit" is my furthest d/s radiator. But maybe the second pump is what is helping here. Tbh, I didnt really notice a substantial difference when I upgraded my main pump from a 15/60 to the 26-50r.
I've upgraded a significant portion of the u/s pipes to 22mm, reducing to 15mm just before the radiators. I've got an ABV, but this only kicks in if all circuits are off. Should this be kicking in sooner perhaps to aid the return temperature, or is this masking the problem instead of solving it ?
All in all, the system is heating up ok in the mornings, though I suspect this may be because HW and u/s come on simultaneously, perhaps aiding each other given they have the opposite problems (one's return temp is too high, the other's is too low).
Any guidance on where I should go next in terms of trying to get this working as it should - i.e. each zone able to independently function. Or is this an impossibility ?
Thanks.
The d/s zone seems to work absolutely fine since adding the second pump (previously had problems with radiators not warming up). It heats up nicely within 20 mins either independently, or with the other zones open too.
The problems I have are as follows:
1) The HW zone when calling for heat on it's own works for a long period of time, but eventually starts short cycling to get fully up to the stat temp. I suspect this problem is due to my removing the additional radiator on the HW zone, which was recently done. I intend to add it back in. My question is, given the power requirement for all three zones, is there a solution to range rate dynamically when only the HW zone is calling for heat ? I understand a VR65 can independently control the HW flow temperature, but can it also control the output power to lower it ? Eg. If I range rate the boiler to 18KW, then the short cycling disappears. Am I right in saying the extra radiator should also alleviate this problem once again ?
2) The u/s zone seems to have a flow problem. If I have only the u/s zone calling for heat, I can see the flow / return delta is quite large. The return temperature seems to take an absolute age to increase. This frequently causes an S53. What else can I do to try and resolve this - would a second pump on the u/s circuit help ? Do I need a larger pump than the 26-50 ? What's strange to me is that all of my d/s radiators drop from u/s, so the "index circuit" is my furthest d/s radiator. But maybe the second pump is what is helping here. Tbh, I didnt really notice a substantial difference when I upgraded my main pump from a 15/60 to the 26-50r.
I've upgraded a significant portion of the u/s pipes to 22mm, reducing to 15mm just before the radiators. I've got an ABV, but this only kicks in if all circuits are off. Should this be kicking in sooner perhaps to aid the return temperature, or is this masking the problem instead of solving it ?
All in all, the system is heating up ok in the mornings, though I suspect this may be because HW and u/s come on simultaneously, perhaps aiding each other given they have the opposite problems (one's return temp is too high, the other's is too low).
Any guidance on where I should go next in terms of trying to get this working as it should - i.e. each zone able to independently function. Or is this an impossibility ?
Thanks.