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Discuss Pump constant pressure or proportional to the thermal output in the Central Heating Forum area at PlumbersForums.net

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Hi

I have a worcester boiler and one of the settings is 3-d1 (Pump range map) as attachment below

Now the installer has set it away from the default of 250mbar to proportional to the thermal output and also changed 3-d3 to 30%.

The issue I now have is that with the zones fully open then sometimes the automatic bypass is cutting in (noisy and hot), even when set up at its max 0.5 setting. It is doing so even more when zone valves are near closed (in the constant setting it did not do this).

Now I have read somewhere that if you have an automatic bypass the it should not be set proportional but to constant as otherwise the proportional one can go to its max setting.

I have tried ringing Worcestor technical (twice) but after 45 minutes on hold each time had to give up (phone was running out of charge).

Can anyone please let me know what this option actually does and whether it needs to be set back to its default of 250mbar.

Thanks
Colin
 

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Hi Colin (again),

The proportional settings referred to above have got nothing to do with a ABV having a problem with a pump set to proportional pressure (PP) mode.
IMO your pump settings are (now) being dictated to and are proportional to the thermal output of the boiler or something like that and it must be a 7M pump because a ABV can't open if set to 0.5bar if the pump isn't developing > that even with everything opened up and as you say will be even worse with the TRvs throttled in.
I would set d.1 to 5, 350mb as I think setting 3 at 250mb is too low, it doesn't matter then what setting d3 or d4 is, as d1 is now at a setting other than 0.

Also the ABV cannot now open except you reduce its setting to < 0.35.

I thought that the increase to 30% was referring to the boiler output in your Evohome thread.
 
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Hi Colin (again),

The proportional settings referred to above have got nothing to do with a ABV having a problem with a pump set to proportional pressure (PP) mode.
IMO your pump settings are (now) being dictated to and are proportional to the thermal output of the boiler or something like that and it must be a 7M pump because a ABV can't open if set to 0.5bar if the pump isn't developing > that even with everything opened up and as you say will be even worse with the TRvs throttled in.
I would set d.1 to 5, 350mb as I think setting 3 at 250mb is too low, it doesn't matter then what setting d3 or d4 is, as d1 is now at a setting other than 0.

Also the ABV cannot now open except you reduce its setting to < 0.35.
Hi John

I got through to Worcester Technical (had to use the installer option) and he thought it should be constant pressure but not 100% sure (I had emailed the other day and they said they wanted to talk about it with me but not got back, he thinks its has been escalated higher for someone to look at). He has gone away to gather more information and will, hopefully, be ringing me back with more information.

I personally think (probably wrongly) that the proportional mode will be sending out its max at some point and as valves are closing this is enough to divert it all though (at which point the boiler stopped heating and even with demand it did not seem to do a pump run on but I may not have caught that properly (boiler downstairs, bypass upstairs).

Why do you think the default 250mbar is too low (what does it affect?)

Re the ABV setting, are you saying that at setting 3 (250mbar) it would need to be set to < .25 to come on and for setting 5 (350mbar) it would need to be set to <0.35. If so do I set it slightly higher or lower than the 0.5 (concerned as it came on with proportional when set slightly under 0,5!)

BTW thanks for all your help recently.

Thanks
Colin
 
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When did someone decide on the pump set to 0?. did they also get confused with the suggestion

"There appaears to be a parameter 5-A3 "Minimum boiler output (heating and DHW)" whose default is 10% (and max is 50%). I will be asking the installers (who did the boiler and Evohome) whether this needs to be set higher (perphaps 20-25% or higher?) so the boiler does not modulate so low at the start (especially as the Evohome will be in control)"

Thats the setting say 30% I would increase as you really want to get this boiler up to its max ASAP and let evohome do the rest.

With all zones opened up I just think it (250mb) may be a little low it mighn't give sufficient flow, 350mb might be more appropriate but it possible doesn't require it, it certainly will not do amy harm to set it to 350mb.
I would keep this ABV out of the picture just now (setting at 0.5) as suggested by others as the boiler internal bypass is probably ok.
 
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When did someone decide on the pump set to 0?. did they also get confused with the suggestion

"There appaears to be a parameter 5-A3 "Minimum boiler output (heating and DHW)" whose default is 10% (and max is 50%). I will be asking the installers (who did the boiler and Evohome) whether this needs to be set higher (perphaps 20-25% or higher?) so the boiler does not modulate so low at the start (especially as the Evohome will be in control)"

With all zones opened up I just think it (250mb) may be a little low it mighn't give sufficient flow, 350mb might be more appropriate but it possible doesn't require it, it certainly will not do amy harm to set it to 350mb.
I would keep this ABV out of the picture just now (setting at 0.5) as suggested by others as the boiler internal bypass is probably ok.
Hi John

Allegedly the boiler does not have a bypass itself. Their instructions say that if using radiator zone valves then an automatic bypass is required but it is up to the installer to decide what setting it needs!

The installer was on to Worcester and they said to put it into the mode 0 (as an afterthought), hence why I emailed them last night to see why they said it. I thought changing 5-A3 to 20% would be sufficient for my needs (not the 33% Worcester said nor the 30 that the installer set)

I am somewhat wondering about the ABV value as the installer set it (just above 0.4 ) but then said it was up to me to adjust to suit as I live here!

For now I am setting back to 0.4, will have to wait until the controller starts cycling the boiler with valves shut lower and twiddle then.

Thanks
Colin
 
OK then, If you require to set the ABV where it will have some effect then suggest setting it to 0.3/0.325 if you have set the pump to 350mb or set it to 0.225 if pump set to 250mb, I definitely think you should set the pump to 350mb now though if bringing the ABV into play, the position of the ABV well away from your boiler means that the differential pressure across it will vary with different flows so as the TRVs close in it should open some more and hopefully not too much, as you will now be taking a little heat from the system then maybe think about increasing that 5-A3 to 30% or higher, you won't be wasting heat as the 300/400 watts emitted by the ABV piping will be absorbed by the house.
 
OK then, If you require to set the ABV where it will have some effect then suggest setting it to 0.3/0.325 if you have set the pump to 350mb or set it to 0.225 if pump set to 250mb, I definitely think you should set the pump to 350mb now though if bringing the ABV into play, the position of the ABV well away from your boiler means that the differential pressure across it will vary with different flows so as the TRVs close in it should open some more and hopefully not too much, as you will now be taking a little heat from the system then maybe think about increasing that 5-A3 to 30% or higher, you won't be wasting heat as the 300/400 watts emitted by the ABV piping will be absorbed by the house.
Hi John

Is it really only 300/400W when the ABV cuts in as the pipe between it gets blooming hot (red hot)

As ABV are proportional I presume that in normal operation when valves are near closing that it will just feel a little warm but some heat will still flow to the radiators?

At 250mb the ABV will open at at setting of approx 0.35 when tested just now (though will monitor it).

Thanks
Colin
 
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Somewhere around 50W/M for uninsulated 22mm copper and maybe 10W/M for insulated I read sometime.
The rads will get warm of course, the evohome will soon make allowance for this.

So you've set the pump to 250mb,the 5-A3 to 20% and the minimum firing time to 5Mins.??.
 
Somewhere around 50W/M for uninsulated 22mm copper and maybe 10W/M for insulated I read sometime.
The rads will get warm of course, the evohome will soon make allowance for this.

So you've set the pump to 250mb,the 5-A3 to 20% and the minimum firing time to 5Mins.??.
Hi John

Until Worcester confirm (still not been rung back yet but I know they are busy), I have set back 3-d1 to default of 250mbar, 5-A3 to 25%.

As I have now increased the start modulation to 25% (7.5KW), I have reduced the Evohome on time from 5 minutes to 3 minutes (seems to work at the moment - takes a couple of 10 minutes goes to get to around 60 degrees but that is nowhere near as bad as over 2 hours it was on 10% - though I will have to monitor it better in case I need to up it (to 4 or 5))

Thanks
Colin
 

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