Central Heating Pump : Question about performance degradation

[testpilot]

I have a Grundfoss SuperSelectric UPS 15-60 (3 speed) pump in my system.
Quite a few of the radiators are barely warm, with the rest getting hot, but not as hot as normal.

Have done all the usual, venting and valve closing and opening on the rads to no avail.

The motor has always been on speed 2, but I did try 3 (faster) a few years ago when I balanced up the system and found that the pump pushed water up the vent pipe into the header tank... i.e. it was too fast.

With the current problem I tried speed 3 again, but it no longer pushes water up the vent pipe
(I thought there could be a blockage, but this proves otherwise)
The pump sounds OK, and the 3 port valve seems to be diverting properly


So to the question.

Do pumps degrade in terms of pumping power?

 

[mickie]

Yes..

 

[tamz]

A super selectric is about 70 in pump years (about 20 at least in real years) . Its past its best. Nothing lasts forever including your system.

 

[jtsplumbing]

Pump, But your system may also need cleaning.

 

[testpilot]

Update:-
After removing the motor assembly off the 3 port valve, I discovered the valve shaft was too stiff to turn, so the motor was only able to turn it to a 'non standard' position.
Normally you can turn it with little resistance.
New valve was the solution