BG Multihead G Pump - Replacement Required?

[jamesmc]

Hi All, I live in a 4 bed detached house with 14 rads and small bore (not microbore) piping. Ever since moving in, the rads get warm but not hot. Had a plumber visit for a quote this week and he suggested that the BG Grundfos Multihead pump isn't up to the job in terms of flow around the system. Not sure if this is correct, so thought I'd ask on this forum . I've also been checking out Grundfos pumps (these seem to have a good reputation) for a possible replacement. Trouble is, I can't see what the difference is between the Multihead and say a Grundfos 15/60. If anything, the ratings on the front of the Multihead suggest it is a more powerful pump?

 

[nickso]

the multihead G is intended as a general replacement for any pump. the speeds and "power" are only slightly different from the 15/50 or 15/60.

is the pump noisy? is the system water clear? the pump could be running slow, have you tried putting it up a notch to see if there is any temporary improvement? could be on max already.

 

[scatmanjohn]

Same pump, different colour

 

[namsag]

Speed 3 on a BG multihead pump is equivalant of a 15/60 , Hence the name multihead.
Also the recent multi heads are grundfoss pumps originals with black knob in middle where mysons(silver screw is grundfoss)

 

[palerider45]

just out of intrest was was his qoute and what was he going to fit

 

[bengasman]

What is the total length of rad panels?( each metre is roughly 1 kW)
What boiler do you have?
Is your pump currently set at maximum?

 

[twgas]

Can't see that your existing pump is not big enough.
What exactly were you getting a quote for - I'm not asking for price, just for the work you want done.

 

[jamesmc]

Cheers for the quick replies guys. Tackling each question in turn;
- the pump isn't noisy and it's on max setting already (i.e. 3)
- definitely a Grundfos multihead pump
- quoted £300, didn't specify the pump that would be fitted
- boiler is a Stelrad Ideal NF60
- will have to measure total rad panel length, will post later
- asked for a quote on flushing the system, guy came out and recommended a pump change instead

Thanks again for your help!

 

[doitall]

What is the size of the pipe in and out of the pump. Assuming it's 22mm when does it split to 15mm, and how many rads on each leg.

Sounds like it just needs balancing properly.

 

[jamesmc]

Hi doitall, 22mm in and out of the pump. Just had a look in the airing cupboard and there is a split to 15mm about a 1m away. Confused by this though as the split has 2 x 22mm pipes and 1 x 15mm pipe. Suspect I'm looking at the wrong thing, will post a photo tomorrow. If it's a balancing thing, wouldn't some of the radiators be warmer than others? They all reach pretty much the same sort of temperature (i.e. warm but not hot).

 

[ollski]

It doesn't really matter what pump it is if it's full of muck and running slow it won't heat the system. A new multihead is adequate for your system though.

 

[jamesmc]

Answering final couple of questions as promised;

- Total of 11.36m of rad panels (so I guess 11.36kW).
- Upload of pic 22mm to 15mm split in airing cupboard (not sure if this is what you were on about doitall?)

 

[bengasman]

Answering final couple of questions as promised;

- Total of 11.36m of rad panels (so I guess 11.36kW)....

It's not that exact. but close enough to determine that the dissipation is somewhere between 10 and 13 kW, presuming that you have counted double panel rads as 2 panels; if not, it's easy enough to correct.
The purpose of the exercise is to make sure that the total output of the rads is not significantly higher than the output of the boiler, which would cause the rads to be underheated. As your boiler is around 18 kW, this does not seem to be the problem.
My guess would be that on a system this size, any odd pump would do, and no need for 15-60.

That leaves:
pump dying
blockage
"heatleak" through a faulty bypass.

 

[nickso]

Answering final couple of questions as promised;

- Total of 11.36m of rad panels (so I guess 11.36kW).
- Upload of pic 22mm to 15mm split in airing cupboard (not sure if this is what you were on about doitall?)

you havent told us if the system is full of muck. if it is then that could be a problem. that air seperator could be choked.

 

[D_Hailsham]

Do you have a magnet? If so hold it against the pipes and the air separator in your photo and see if it sticks. If it does the pipes/air separator are blocked up. They will probably need cutting out and replacing.