Noisy hot water pipes in unvented system

[Jonathan1]

I recently had an Ariston unvented, indirect hw tank installed, replacing a gravity fed tank. After a couple of months without problem we now get a loud groaning when the hot water taps are opened. It doesn't happen every time, but seems to occur most if there has been a long interval between the last hot water draw-off. Is it likely to be caused by pipe expansion and rubbing, or could there be a problem with the pressure balance valve?

Thanks,

Jonathan

 

[doitall]

Where is the groaning coming from.

Get the installer to check it out.

 

[meldrew's_mate]

Turn off the mains supply to the cylinder at the pressure reducing set. When a hot tap is turned on the water should run for several seconds before petering-out. If it stops almost immediately you could have lost the internal air gap, which will need regenerating - this is easy to do and will be in the instructions. My guess (and that's all it is at this stage) is the groaning is the PRV chattering as the downstream pressure fluctuates wildly as water is drawn, the noise is the pipework resonating at certain flowrates.

I'm sure I'll be shot down in flames if the Ariston doesn't have an internal air space, in which case check the external expansion vessel charge pressure is correct

 

[doitall]

We covered this somewhere before so may pay you to do a search.

Could be the pre-charge in the vessel 3.5Bar.