Do Grundfus Pumps lose efficiency?

[kingimuk]

I have looked around the wiki and forums but do not see a specific answer I am looking for. Forgive me if it is already out there.

The distant radiators at the ends of the two branches of my system are struggling to get heat. Don't believe it is sludge etc as the water was clear a couple of months ago and has sentinel in it. Used to work ok and my gut feeling is that the pump no longer seems to have the force it used to have.

Can this happen to a pump? Clearly it would be easier if it just stopped working altogether.

System is Y-plan and the water circuit functions without issue. Have shut down all rads and then turned on one radiator at a time. They do all then emit heat at a very hot temperature but after what seems a long time given I now have the pump on speed three. When it was installed (9 years) you could never use speed three as it was too fast/noisy.

Pump?

 

[TeaTime]

Have you noticed this straight after your power flush or before?

https://www.emergencyplumber.uk.com/plumbing/central-heating-pump-problems/

 

[kingimuk]

Hi TeaTime

I already looked at link you gave me. I intend to try to bleed the pump tonight and see if I can rotate the shaft easily or not.

My main question is - how do pumps fail when they still appear to be rotating? Is it possible that they start going slower? Something I cannot get my head around - as I expect the speed to be locked to the mains frequency (50Hz) or 3000rpm - so how can the water flow be slower?

As I said it would be better if it was not spinning at all.

There has been no flushing since re-filled in 2010 with sentinel and water is still straw coloured.

Thanks

 

[TeaTime]

This old thread has some interesting info.

You may find your answer in here.

//www.diynot.com/forums/viewtopic.php?t=51136

 

[Weedrip]

Pump impellor can become blocked over time the veins are quite narrow and they trap small particles and then collect more.

isolate pump valves undo the 4 allen bolts and gentle release the head from the body.

do be sure the pump valves are isolating properly first tho.

a paper clip can be bent to poke out the veins on the impellor if that is the problem.

 

[MANDATE]

Relative had similar problem. Removed radiator and cleaned it. Made no difference!
Checked and closed the by-pass a little. Cold radiator became warm but not hot.
During this work pump stopped working so removed it.
Found scale had formed around inlet and outlet or I face.
What should have been around 20mm orifaces were reduced to about 7 or 8mm dial.
Obviously this acted as resistor so new pump installed.
The valves each side of pump were in similar condition and these were also replaced.
This action resolved the problem.

 

[JohnD]

The brand of pump is immaterial.

You say the system has Sentinel in it. It might still have years of accumulated sediment. Or have you cleaned it out?

When did you balance the radiators?

 

[oilboffin]

Clean out the impeller the drain down the system refill with a double dose of cleaner, run the system at a high heat for two weeks then flush again for three or four hours then start draining the dirty water out and individually
run the water through each rad when all runs clear try the pump it should be all plays good luck lot of work but worth it

 

[Agile]

The brand of pump is very important!

To check the pump see the FAQ on this site for the "finger test".

Of course while doing the finger test you will also be inspecting the impeller for dirt.

Many pumps lose torque because the capacitor loses capacitance. That's a particular problem with Circulating Pumps CP53 and CP63 pumps. Rare with Grundfos though.

With the right meter you can measure the capacitance of the part in the pump if its low torque.

Tony

 

[kingimuk]

I appreciate all the useful comments. I do hope I find it is the pump when it comes out as I have eliminated most other things. Just couldn't see it would be the pump - now I do see! Will report back when I know more.

IK

PS: I do have the means to check the capacitor while I am at it.

 

[kingimuk]

Have taken just the pump head off and was incredulous as to how blocked the veins were!

Was also surprised as to how narrow the gap was where the water is expelled from the pump in a centrifugal manner. I thought the pump would be more manly than it actually is.

Cleaned out the narrow chambers between the two (plastic?) plates where the water is expelled with an elongated paper clip and the sludge was mainly brown. This is like the 'muck' that build up in the system header tank (vented gravity feed).

Whether the pump is spinning at the correct speed I am not sure as I have it running on three still - but the radiators now get properly hot when required and quickly too.

I will monitor for now, but maybe the pump veins will block again.

IK

 

[muggles]

Sounds like your system needs powerflushing

 

[JohnD]

or at much much much lower cost, start with a DIY chemical clean and see if that does the trick.

If you are handy and can afford £100, fit a system filter as well.

Brown sludge is only very faintly attracted to magnets, so you will need one that can trap non-magnetic particles as well as black. The chemical is likely to loosen a lot of both.