Posted by: @jamespa

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Is it possible there is air still trapped in the system.  Mine took a month to clear and despite the presence of an auto bleed valve one radiator needed daily bleeding.  Alternatively have you got an almost shut valve somewhere through which the water is being forced causing noise.  Are all, or at least most, of your TRVs set to max so constantly open. 

Flow through pipes should be close enough to silent not to matter so the noise is more likely to be a valve or bend or air or such like.

After installation the system did develop a noise in the volumizer and that turned out to be a bleed valve. Which when fixed caused a squeal in the balance pipe! Engineer was here so immediately knew what to adjust. In water heating mode there is no noise. Only when the two port switches to CH. I just checked the rads and everything was open apart from the lockshield in my bedroom which had a couple of turns on it. So I reckon that is another small improvement made thanks. No air in the rads.

Most of the noise comes from the outside pipes going up and over my bedroom and then down the other side to the downstairs rads. So I'm rather surrounded by pipes and susceptible to any noise in the system.

Posted by: @radwhisperer

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Most of the noise comes from the outside pipes going up and over my bedroom and then down the other side to the downstairs rads. So I'm rather surrounded by pipes and susceptible to any noise in the system

ah - not the greatest routing.  Is it possible to insulate and/or isolate the pumps from the structure?

@jamespa Small mid-terrace so everything is is in closr proximity. Only thing I could do is try to swap the cheap plastic pipe clips for rubber isolating ones.

However I think that lockshield was contributing as it seem quieter when it turned on this morning. Just need a properly cold morning to hear it at it worst!

Posted by: @radwhisperer

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However I think that lockshield was contributing as it seem quieter when it turned on this morning. Just need a properly cold morning to hear it at it worst!

Thats encouraging.  As I say normal motion in pipework should be inaudible, its valves and bends that cause noise.  Swept bends are better than elbows incidentally, but more trouble for the plumber.

Posted by: @jamespa

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Thats encouraging.  As I say normal motion in pipework should be inaudible, its valves and bends that cause noise.  Swept bends are better than elbows incidentally, but more trouble for the plumber.

My MMI is in the loft but I checked the pump flow rate when running the DHW cycle and it was 25 l/h and I could hardly tell it was running. So now I know where to look for any further noise reductions (if even required) cheers.