BG Grundfos multihead flow rate

[Ben565]

As part of a recent overhaul of my open vent central heating system, the old British Gas Grundfos Multihead pump was replaced with a new Grundfos UPS3 15-50/65.

The new pump, even on setting I seems far to fast for my system. Even on setting I the sound of water being forced under pressure through the rads and pipework is loud and can be heard throughout the house. If the DHW comes on at the same time as the central heating is on then the noise quietens down somewhat. I've also noticed hot water in the expansion tank.

Of course these things could have other causes, but I read somewhere that speed I on the new pump is about the same as speed III on the old BG Grundfos pump. Well for sure speed III was too fast and loud on the old pump, I think we had it on I or II . Can anyone confirm the new pump is more powerful and faster flowing than the old one ? and is there a new pump with similar speed/flow to the old pump ?

 

[Johntheo5]

The UPS3 15-50/65 is a very powerful pump as you can see from below but there are a few options which should satisfy your needs without noisy operation.
Would suggest PP2 (proportional pressure) as first choice and if too weak suggest CP1 (constant pressure).
Your present choice of CC1 will run at a 3.9M head at a typical CH demand of say 0.8m3/hr, 13.3LPM, whereas PP1 will only provide this at 2.4M and CP1 at 3.0M so one of these should do the job IMO.

If the demand is actually 13.3LPM at 3.9M, then PP2 will provide 10.1LPM at 2.23M and CP1 13.3LPM at 3.0M.

 

[Ben565]

Thanks for the info, just having a look in the manual and it says

Note: Proportional-pressure mode is not recommended in heating systems that includes an automatic bypass valve to ensure a minimum flow for the heating appliances.

and I think I do have an automatic bypass valve.

I'll give CPI a go though. Failing that presumably Grundfos do a lower powered version of that pump ?

 

[Johntheo5]

Give CP1 a go and see what happens, if you locate the bypass see what setting it's on

 

[Johntheo5]

I'll give CPI a go though. Failing that presumably Grundfos do a lower powered version of that pump ?

Yes, you can get lower output Grundfos, however the problem with all A rated pumps is that the constant curve CC modes are NOT, they act like a constant pressure mode right in the region where you require (for ABV control) a curve like the traditional 3 speed pump which increases with reducing output, you can install a manual bypass but this will allways bypass even when not required.
If you dont use TRVs and only need a bypass on pump overrun when the zone valves close then a NO (normally open) motorized valve installed as a bypass and wired to the terminal block where the zone valve end switch(s) are paralleled will only open when all zone valves close but will close when any one zone valve opens should work OK.

 

[Ben565]

CP1 seems to be much better thanks

I've got an S Plan system, with DHW and CH zone valves, and TRV's on all but one radiator.

 

[Johntheo5]

You might check your ABV setting and note the boiler flow temperature on pump overrun (if installed) when all zone valves close.

 

[Ben565]

I did have someone come take a look at my system and check out the potential causes of hot water in my expansion tank. They told me it's because I'm running the boiler constantly, all the TRV's are closing, and I have the pump speed set too low (speed I). For reasons they didn't want to go into, that's apparently causing hot water to end up in the expansion tank. And I should leave the pump set on speed II.

Well I left it on speed II for about a day before I got totally fed up of the row it made. And I noticed that I still got hot water in the expansion tank anyway so it made no difference.

I've experimented with different pump settings, speeds I, II, III all make a tremendous row and I get steaming hot water in the expansion tank. Setting CP1 as suggested here is much quieter, and guess what, no hot water in the expansion tank ! so I've left it on that for now.

I did try Proportional flow mode (making sure the CH zone valve was open) and this is even better, definitely want to give this a try but from what I've read I'll need to set the ABV wide open, and put a Taco setting valve in series.


I haven't checked the ABV setting, but the installer did set this up, so I'm assuming it's correct. I do have a pump overrun (which is why I need a bypass) Gonna have to get a thermometer to measure flow return temps

 

[Johntheo5]

PP2 should be your best choice IMO, PP1 probably too weak.
The Tachosetter is a manual bypass that shows you the flowrate.
Also reread the last paragraph of my post #5.

Sometime maybe post a photo of your venting and cold feed arrangement.

 

[Ben565]

yes agree about PP1 it seemed a bit too weak when I tried it, PP2 seems perfect.
Ah yes re-read what you said about wiring a valve up on the bypass to open when the CH zone valve closes. I've got two zone valves so it would have to be if BOTH DHW and CH zone valves are closed, then open the bypass pump overrun valve.

Pictures attached, it looks to me like the vent pipe isn't high enough above the water level. Both the vent pipe and the FE pipes are hot, although I never seen or heard water running out of the vent pipe into the tak.

 

[Johntheo5]

Ah yes re-read what you said about wiring a valve up on the bypass to open when the CH zone valve closes. I've got two zone valves so it would have to be if BOTH DHW and CH zone valves are closed, then open the bypass pump overrun valve.If the supply to the NO valve is taken from terminal 10 then that should do?.

If the supply is taken from terminal 10 then should work OK?.

Pictures attached, it looks to me like the vent pipe isn't high enough above the water level. Both the vent pipe and the FE pipes are hot, although I never seen or heard water running out of the vent pipe into the tak.

The vent shouldn't be immersed in water.
Can't see where the cold feed is teed into the system but might be done like below.

 

[fixitflav]

I did have someone come take a look at my system and check out the potential causes of hot water in my expansion tank. They told me it's because I'm running the boiler constantly, all the TRV's are closing, and I have the pump speed set too low (speed I). For reasons they didn't want to go into, that's apparently causing hot water to end up in the expansion tank. And I should leave the pump set on speed II.

Very doubtful that's the reason IMO, but it needs sorting. Is (hot) water coming out of the vent pipe? If so, could be a partial blockage between the cold feed and vent connections (depending on how it's all piped up).

 

[Ben565]

I had my doubts about that too, but then I'm not an experienced tradesman. The vent and FE pipe tee off close to each other just before the pump. The system has recently been powerflushed so it ought to be fairly clear.

I can't see any hot water coming out of the vent pipe, that's not to say it isn't happening though.

There's no hot water in the expansion tank if I leave the pump set to CP1 so I'm leaving it like that for now, until I can get someone to take another look and probably redo some of the pipework in/around the expansion tank.

 

[fixitflav]

I had my doubts about that too, but then I'm not an experienced tradesman. The vent and FE pipe tee off close to each other just before the pump. The system has recently been powerflushed so it ought to be fairly clear.

I can't see any hot water coming out of the vent pipe, that's not to say it isn't happening though.

There's no hot water in the expansion tank if I leave the pump set to CP1 so I'm leaving it like that for now, until I can get someone to take another look and probably redo some of the pipework in/around the expansion tank.

You could try increasing the pump speed temporarily as a test, see if it causes overpumping. Does the cold feed pipe come in up and under? That's the correct way, if it tees off the top of the pipe it can allow convection of hot water into the F/E tank.

 

[Ben565]

Does the cold feed pipe come in up and under?

I don't know to be honest

Yes will try increasing the pump speed as a test and monitoring what's happening in the tank.