Adding a second Expansion Vessel?

[JasetheMace]

It’s a Megaflow, don’t they have an internal air gap?

That would be my guess! If expansion vessel is 4m away, more likely to be heating expansion vessel rather then hot water.

 

[chris watkins]

That would be my guess! If expansion vessel is 4m away, more likely to be heating expansion vessel rather then hot water.

The OP has their G3 so I would expect them to be capable of knowing the difference between heating & hot water vessels.

Even if it is a Megaflo with an internal air bubble for expansion addition vessels can & are often added, for instance when the baffles has failed or there is a secondary return installed which increases the amount of water being heated.
The worry here (as far as I can tell from the description) is that it has been installed on the cold feed 4 Metres away from the cylinder so it is very likely to be on the wrong side of the check valve which is built-in just before the pressure relief safety valve. If it is then this will isolate the vessel from the source of expansion so it can't work & the pressure will continue to cause the safety valves to open!!

 

[Duker996]

All sorted now chaps.

As Gary said it was due to not having balanced supplies at the new shower and them clearly not fitting check valves. There was no way of me getting to any of the shower pipes so a 3bar pressure reducing valve on the incoming main has cured it.

No idea why the vessel, relief valve, reducing valve etc was placed in a small roof space 4 metres away but it is all correct and how it should be, no check valve between the vessel and cylinder.

First time I've seen this issue in my 19 years plumbing, hence why I was a bit baffled by it!

Thanks all for the help