Grundfos 15/50 pump

[tryitandsee]

Have bad flow in a micro bore central heating system, open vented , threeway mv.

We think we have narrowed it down to the pump.
The system was very dirty, sludge etc in rads which we have taken off and flushed through in garden.
My questions are, as pump spinning from looking/feeling at pump bleed screw and all the signs that it is working,

can the vanes in the pump impeller get blocked with crud. (Like crawl swimming with your hands not cupped, as best as I can describe it)

can the impeller wear out.

If we give the system an easy circuit to flow round, in this case the hw circuit it works fine.

If we let it do the ground floor rads (pump in airing cupboard upstairs landing) they get reasonable but the flow pipe returning to the boiler never gets that warm. If open rads to upstairs it gets to the rad valves only.

For the sake of a new pump at £80 it's probably not worth fannying about, but as I am helping a friend it's me that feels awkward when installed, it makes no difference.

 

[JohnD]

yes, a pump and its valves can clog with black sediment. So can pipes. If you have already found sediment in the system, it would be a good idea to run it for a few weeks with Sentinel X400 in it. This is a very mild, non-acidic cleaner that softens and loosens sediment and sludge so that it is washed away in the water. You know it is starting to work when the water goes jet black with loosened sediment.

unlike some more aggressive cleaners it does not need to be neutralised afterwards, and does not do any damage even if you forget to drain it out (though this will negate the cleaning effect as the dirt will settle back again eventually)

It is worth doing this whether or not you later change the pump, it will only cost about £15. You leave it circulating for up to 4 weeks before draining, rinsing and refilling. Use an inhibitor such as X100 on final fill.

btw if you are getting bad flow on the radiators, check that the 3-way valve is not allowing flow to leak through the HW cylinder pipe once the cyl is up to temp. And look at the F&E tank to check it is not pumping over. Bale out any mud from the F&E and sponge it clean.

 

[tryitandsee]

Thanks JD
I think that would be a good idea first and let this suspect pump run with it for a while. I can always change it later on.