Pressurized plumbing noise

[crazy600]

Has anyone any ideas?
I have this loud groaning noise coming from the area of my pressurised hot water cyliinder, which includes expansion vessel.
I had this problem a while after this new system was put in, had many plumbers look at it, and there only sugestion was to move the grunfos mq pump to the ground floor(it was orig in attic with cylinder) and turn expansion vessel on its side.
Did this, with much expense and hey presto problem gone! now 6months later the noise is back again (it would wake the dead). help please"

 

[Puddle]

Well maybe first thing to do is check expansion vessel does not need re pressurising again 🙁

imho

 

[crazy600]

Well maybe first thing to do is check expansion vessel does not need re pressurising again 🙁

imho

Thanks puddle did that, also changed the temp/non return valve, which is between the pumped mains water and hot h2o cylinder from spring type, to open shut valve type, moved the cold water to also go through the non return valve. Now I have the noise on both the hot and the cold.
Checked the cylinder temp to make sure it was'nt cooking and it's fine, also checked the pump to make sure there was no dirt blocking the line. run out of ideas. I'm at my witts end. The only other suggestion seems to put a pressure reducing valve before the non return which we could try to throttle down and see if it makes a difference.
😕