Grundfos pump making unusual sound/boiler not coming on

[Stephen JW]

Agree, I have 10 rads (no balancing), OV system, on a 4.4M PP setting (Wilo Yonos Pico) which gives ~ 14LPM @ 3.2M.
The UPS3 flows 18.3LPM @ 6.3M on CCIII & 18.3LPM @ 5.0M on CCII.

As a matter of interest what model Grundfos do you have?.

Hi John

So it seems that you were correct when you deduced that it was most likely a faulty pump back in post #32! Just a pity that it took our guy so long to concur and change it.

He replaced the pump and rebalanced the upstairs rads 2 days ago. He left it running on CCIII.

The pump was near silent running in CCIII and there was no vibration or resonating in the system.

Yesterday we tried CCII and that works perfectly as well.

We have set the TRVs between 2 & 3 and the boiler to 3.5.

All radiators are hot (top to bottom, corner to corner) within 20 minutes.

Boiler is running smoothly and quietly. We can’t remember the system ever running as quietly as it is now.

Once again thank you so much for all your help with this. I have learnt so much from you, which was an invaluable help in arguing the case for it being a faulty pump.

 

[John.g]

That's great to hear.
You could also run it on CPII which gives 95% of CCII flowrate and will save a extra bit of energy when the TRV's start throttling in. Unfortunately, the PP settings which were primarily designed for TRV operation are practically useless on this pump as they are too low except that you have very large flow and return manifolds but I suppose no harm in trying, its only a button push. IMO the DAB Evosta3 is a far better choice ( Ithink, made or owned by Grundfos) as not only has it higher PP settings but also displays the pump head and flow rate.

 

[Stephen JW]

Ah that's well worth knowing. Will definitely try CPII next. Thanks again for sharing your expertise!
Kind regards
Stephen