Hi All,

Well I think that's what it is. It looks similar one of these

https://www.unventedcomponentseurope...-95605886.html

In my situation the large black bit is positioned to the left and the other ports are
Top - cold water feed to house
Bottom - mains water feed from outside
Right - connected to top of h/w cylinder (it is a mega flo type thing for mains pressure hot water)

The leak is coming from the big black bit but not at the end somewhere between the brass bit and the end.

I have done some googling and there seems to be a mix of views
1. This is normal and that's what happens when the pressure is high. Seems odd to me and mine continually drips. Also not sure what pressure is too high - boiler circuit is set at 1.5 bar and inbound pressure is not great
2. It is because the expansion vessels have run out of air. I appear to have 2. One in the inbound supply side and one on the circuit coming out of the boilers. Some people seem to say to just check them and if low too them up (not sure to what) with a tyre inflator (presume the little compressor thing I use to pump tyres up). Others say this is very dangerous. Also TBH not sure what the purpose of either is and therefore which one is likely to be it. If safe, I could do both of course.
3. The valve is faulty and it needs to be changed by a qualified person as could be dangerous.

I have done a lot of plumbing including designing and fitting the whole plumbing (obviously no gas work!) in our last place and adding to the current one so am pretty able but some of the "this is dangerous" is making me think twice.

Any thoughts appreciated. Also if anyone know why I have 2 expansion vessels and what they do that would fill a void in my understanding too.

Thanks in advance

Lee.