Loads noise from expansion vessel

[finchy01]

I recently replaced a PRV on a cylinder that was letting by. I drained from the T&P valve and a little extra from the doc on the cold feed right before cylinder. I also repressurised the external exp vessel to just shy of 3bar as it was totally flat. I got a call yesterday saying that every ime the use the hot water they get a load noise. I popped in on the way home and it did it when I was downstairs but when he opened a hot tap once I was in the loft it died down very quickly. I turned down the lever valve before the combination valve and released a tiny bit of air from the doc but can see what it could be. I didn't check the vessel charge yesterday which I will do when I go back. It must be something I've done as it started soon after I did the T&P valve but I can't see what. Any ideas?

 

[thereisawizza]

I have a brand new Gledhill horizontal in my loft at home, a lot of the time it rumbles when you draw off hot water, not got round to checking it yet............

 

[Best]

Possibly could be the recharge air you did on the expansion vessel being slightly too high. The EV can't allow much shock if air raised too much. Same happened to me on one job and I released the air pressure slightly to cure it. Don't worry about going down to say, 2.5 bar air charge on a 3 bar mains, or even lower to test if it cures the noise. As you know, the EV is not really a safety component, only the overheat controls, MV and relief valves are the critical parts.
Probably have to consider that your air pressure gauge could be slightly reading wrong, or/and your pressure gauge onto the unvented combination valve could also be reading wrong. Very variable the readings between different gauges.
Try the old fashioned 'pen' type mechanical air pressure gauge as another gauge to test.

 

[townfanjon]

Any expansion vessel noises , just throw the useless hoses away and pipe direct to the vessel in 22 mm copper