Hi everyone, I'm looking for some advice please.
My system has 5 Drayton Wiser TRVs. There are 8 rads over 3 storeys and a 170l unvented cylinder. One of the attic rads is in the same zone as the cylinder so just has a "dumb" TRV on it. The two bathroom rads also remain without TRVs and I ensure that at least one of them (first floor bathroom) is always open. Boiler also has an internal bypass. At 30kW I suspect the boiler was somewhat oversized for this terraced house when installed, but it was previously a heavily occupied house share and one or two radiators have also been removed when it was subsequently reconfigured (there is a woodburner downstairs.)
The smartness of the Wiser system is confined to on/off Relay mode. I've read that I can make the boiler do Opentherm using a board sourced from another country. However I gather it won't be smart enough to heat the cylinder to the required temperature when there is a lower flow temperature for the CH - unless some other modifications are made to the system. So I haven't bothered with that.
Once the house is warm and perhaps only 1 or 2 TRVs are calling for heat (without the cylinder), I've noticed that the boiler fires up and the flow temperature reaches the preset level at the boiler too quickly - causing boiler to go straight into pump overrun/anti-cycling. This seems to be because the boiler fires at the full 30kW for the first minute or so, and only modulates downwards after that. Even if I set a lower heating load (say, 18kW) in the diagnostic menu, it has no effect for the first minute or so.
Ideally, I'd like to avoid such frequent overruns - as a few minutes later another radiator might be calling for heat but the boiler won't come on until the end of its anti-cycling mode. And I'm concerned that this constant overrunning is shortening the life of the components. It actually tempts me to increase the flow temperature at the boiler so that it doesn't reach that temperature before cutting out - but that obviously makes it less efficient...
Is the reason for this entirely down to the boiler not being able to modulate for the first minute (which isn't helped by the boiler probably being oversized in the first place)? Is this a known issue with the Ultracom boiler and can the software on the PCB be reflashed to fix it? Or, would it go away if I was able to get the boiler to work in Opentherm (and separately address the need to heat the cylinder to a higher temperature)?
I'd also be grateful to know if the internal bypass in the boiler is having any impact on this. The radiator calling for heat does seem to get warm before the boiler cuts out - i.e. it's not being bypassed completely. And it won't be the only radiator open (although the other is a chrome towel rail which won't be losing a lot of heat). The boiler manual says the internal bypass is pre-set to 0.25 bar and the max is 0.35 bar. Does it need to be increased, or indeed could it not be closing properly? It does look that a small amount of sludge has leaked out of the bypass valve screw at some point in the past.
I'm also not sure whether the CH has all floors of the house in one loop, or 3 different loops. If the latter there will be a lot of resistance on the top floor if the only radiator on that floor that's part of the CH circuit is manually turned off - which I often do as it gets too hot on that floor. The only other thing I could also try is telling the Wiser controller that I have an oil rather than gas system, as then it will only call for heat 3 times a hour rather than 6.
Thanks in advance if anyone has any other thoughts!
My system has 5 Drayton Wiser TRVs. There are 8 rads over 3 storeys and a 170l unvented cylinder. One of the attic rads is in the same zone as the cylinder so just has a "dumb" TRV on it. The two bathroom rads also remain without TRVs and I ensure that at least one of them (first floor bathroom) is always open. Boiler also has an internal bypass. At 30kW I suspect the boiler was somewhat oversized for this terraced house when installed, but it was previously a heavily occupied house share and one or two radiators have also been removed when it was subsequently reconfigured (there is a woodburner downstairs.)
The smartness of the Wiser system is confined to on/off Relay mode. I've read that I can make the boiler do Opentherm using a board sourced from another country. However I gather it won't be smart enough to heat the cylinder to the required temperature when there is a lower flow temperature for the CH - unless some other modifications are made to the system. So I haven't bothered with that.
Once the house is warm and perhaps only 1 or 2 TRVs are calling for heat (without the cylinder), I've noticed that the boiler fires up and the flow temperature reaches the preset level at the boiler too quickly - causing boiler to go straight into pump overrun/anti-cycling. This seems to be because the boiler fires at the full 30kW for the first minute or so, and only modulates downwards after that. Even if I set a lower heating load (say, 18kW) in the diagnostic menu, it has no effect for the first minute or so.
Ideally, I'd like to avoid such frequent overruns - as a few minutes later another radiator might be calling for heat but the boiler won't come on until the end of its anti-cycling mode. And I'm concerned that this constant overrunning is shortening the life of the components. It actually tempts me to increase the flow temperature at the boiler so that it doesn't reach that temperature before cutting out - but that obviously makes it less efficient...
Is the reason for this entirely down to the boiler not being able to modulate for the first minute (which isn't helped by the boiler probably being oversized in the first place)? Is this a known issue with the Ultracom boiler and can the software on the PCB be reflashed to fix it? Or, would it go away if I was able to get the boiler to work in Opentherm (and separately address the need to heat the cylinder to a higher temperature)?
I'd also be grateful to know if the internal bypass in the boiler is having any impact on this. The radiator calling for heat does seem to get warm before the boiler cuts out - i.e. it's not being bypassed completely. And it won't be the only radiator open (although the other is a chrome towel rail which won't be losing a lot of heat). The boiler manual says the internal bypass is pre-set to 0.25 bar and the max is 0.35 bar. Does it need to be increased, or indeed could it not be closing properly? It does look that a small amount of sludge has leaked out of the bypass valve screw at some point in the past.
I'm also not sure whether the CH has all floors of the house in one loop, or 3 different loops. If the latter there will be a lot of resistance on the top floor if the only radiator on that floor that's part of the CH circuit is manually turned off - which I often do as it gets too hot on that floor. The only other thing I could also try is telling the Wiser controller that I have an oil rather than gas system, as then it will only call for heat 3 times a hour rather than 6.
Thanks in advance if anyone has any other thoughts!