Bypass valve

[Tonygeek]

But am I right in thinking that would not comply with the Building Regs? And I'm no expert, but I don't really understand how that helps with only needing a bypass during pump overrun and not at other times. If one were to go down that route, would it not be more logical to have something like a towel rail instead, which could provide a useful function, as well as being more effective at dissipating the surplus boiler heat during overrun?

 

[denso13]

But am I right in thinking that would not comply with the Building Regs?

Yes, neither does a zone valve. Life is too short...

 

[Johntheo5]

Hi again John.

I can’t see anything in the Installation and Maintenance Instructions about the HEx head loss. The only thing in the specs is “Available pump head at 20C system temperature rise = 2 metres”

I’ve done a set of readings at 60C set temperature but could try to do some at 70C if required:

Target flow temp set: 60C
Indicated flow temp: 63C
Actual flow temp: 67C
Actual return temp: 55C
Burner modulation: 27% (8kW)
Pump modulation: 57%
Pump map setting: 2 (200mb)

Can you have a look again sometime when the boiler is running steadily at the target & indicated flow temps and ideally, those or any other readings above.

 

[Tonygeek]

OK John. I'm taking the opportunity of the colder weather today to check the balancing of my whole system this evening but I will try to do some readings as above asap.

 

[Johntheo5]

OK, thanks.
Why (if you are) are you running with such a low (residual) head of 150mb, 1.5M, it's far easier to balance with a higher head, also, I would think most systems would require at least 200mb to run properly.

 

[Tonygeek]

That's a good question, John, that I have sort of been asking myself - but in a somewhat different way. I dropped the pressure from the default 250mb in order to try to reduce noise from the lockshield on the rad nearest the boiler (it's actually very near). With the system balanced, all the rads were receiving flow and had the same mid-panel temperatures but many lockshields needed to be open just 1/4 turn or even a bit less and, even then, I struggle to get 15C, let alone 20C drop between flow and return. So yes, I have been asking myself why it is that, with the lowest pump map available, I am still needing such small lockshield openings, which are of course then rather critical, and still not achieving 20C drop. If I were to increase the pressure again, would this not just make the issue worse?

I have just been round checking rad flow and return temperatures and there are some adjustments needed but only one rad had a drop of 15C - all the others were less. I have inherited a system that has both very short and very long 15mm pipe runs that I can't do much about because the long ones are buried in floor screed and its pretty impossible to do something different. I do think I shall be able to bring things back into balance at 150mb; it's only out because of disturbing lockshields and not having reset them quite right yet.

 

[Mister Banks]

That's a good question, John, that I have sort of been asking myself - but in a somewhat different way. I dropped the pressure from the default 250mb in order to try to reduce noise from the lockshield on the rad nearest the boiler (it's actually very near). With the system balanced, all the rads were receiving flow and had the same mid-panel temperatures but many lockshields needed to be open just 1/4 turn or even a bit less and, even then, I struggle to get 15C, let alone 20C drop between flow and return. So yes, I have been asking myself why it is that, with the lowest pump map available, I am still needing such small lockshield openings, which are of course then rather critical, and still not achieving 20C drop. If I were to increase the pressure again, would this not just make the issue worse?

I have just been round checking rad flow and return temperatures and there are some adjustments needed but only one rad had a drop of 15C - all the others were less. I have inherited a system that has both very short and very long 15mm pipe runs that I can't do much about because the long ones are buried in floor screed and its pretty impossible to do something different. I do think I shall be able to bring things back into balance at 150mb; it's only out because of disturbing lockshields and not having reset them quite right yet.

I think you’re letting this get overly complicated. Don’t worry about the 20c drop across a radiator as no one gets that anymore. Are you using TRV’s on the radiators, if so that messes up the radiator temp drop as well so just ensure the radiators are balanced and let the TRV’s do their thing.

 

[Tonygeek]

Thank you John. Yes, I'm not chasing 20C really and am being satisfied with 12-15C drop at the rads. Yes, we do have TRVs on 8 of our 14 emitters (not on towel rails or on rads where the room stats are) but I balance with them all at maximum and coolish rooms. Have continued with balancing this am and made good progress - almost there.

On further pondering re low pump pressure requirement, it may be of relevance that we do have 5 or 6 sets of flow/return pipes originating near the boiler, each pair serving between one and four rads so, effectively, 5 or 6 heating 'mains' in parallel. So this may constitute quite a low overall system resistance that the pump is looking at.

I've taken these readings with the whole heating system well settled and on Pump Map 1 (150mb):

Target temp set: 55C
Indicated flow temp: 57C
Actual measured flow temp: 59.4C
Actual measured return temp: 44.9C
Burner modulation: 33% (10kW)
Pump modulation: 54%
Pump map 1 (150mb)

 

[Johntheo5]

Your measured flow temp of 59.4C (dT 14.7C, flow 9.79LPM) gives the best fit for a residual head of 1.5M, strange how the target&indicated temps are relatively so far away from it, anyhow, as long as the boiler stays firing whenever on its minimum output, not a problem.