Can Grundfos UPS2 fail slowly?

[John.g]

And to state the obvious, check water level in F&E tank.

 

[bizzlebest]

Easy way to test remove the pump and open the bottom pump valve a smidge see if any water flows

Thanks for the reply Shaun, must'nt there be some water flow through that bottom pump valve already as it does heat the HWC and radiators? It just does it very slowly and giving f23 errors on boiler. Cheers

 

[John.g]

So the boiler pumps up through the mag filter and onwards to the pump. Should the filter not be before the boiler? Or is that being idealistic. Anyhow, the filter appears clean at the moment, I do it twice weekly.
How would I go about unblocking this? Cutting it out and cleaning it then using compression couplers to it back on? Thanks so much for your time. It's much appreciated.

Ideally, yes the filter should be on the return just before the boiler. It would be very unusual to have two pumps in the system if this is what you are inferring by saying the "boiler pumps up through the mag.filter."
You should carry out the suggestion above by draining off some water and see if the ball cock starts making up water into the F&E tank as rapidly as its being drained off, that will show if the cold feed is clear, at least

Should also have asked if HW circulates without alarming if HW only selected, esure the red gate valve on the coil return is at least 1 full turrn open.