Turning off water draining to make repairs Main Pressure?

[Ginettamad]

Just moved to newish house and within weeks two damp patches have appeared in 2 room ceilings! I have cut a hole out and found a leaking JG speedfit Tee fitted to a grey pipe which supplies HW to a bedroom. Now I thought JG pipe should be white not grey which makes me wonder that the original builders have used none matching fittings throughout the house!
Until I take it apart I cant tell if end seals have been used but our system does run at quite a high pressure. This is a big worry as two leaks are already evident.
Not checked the other damp patch yet but its on the same run line I suspect and its not the central heating.
Now I cant find an internal stop cock so guess I'll need to turn off the house supply from the drive cock but with a main pressure system would I just run off the hot water til it stops before disconnecting HW pipes?
On reconnection will the cylinder just re pressurize itself or is it much more involved? (I realise I shouldn't mess with the pressurising system itself).
Ideally I'd like to repair a dripping tap whilst the water is off and fit a number of isolators too and as few seem to have been fitted and its only an 8 year old house.
H

 

[Agile]

If its an unvented cylinder you should be able to turn off the water to the cylinder only so you can still make a cup of tea!

 

[Terry lambert]

If your sure it's a hot water pipe?

Then yes turn off the supply to the cylinder open the hot taps to run off most of what's in the pipes.

Take the fitting apart and have a look. Is there an insert in the pipe?
Has the o ring got a split or worn? Is the pipe pushed home into the fitting properly?

After your done, close all the taps, turn on the supply, check for a leak and then bleed through the taps starting with lowest first.

 

[Ginettamad]

I found all the jg screw collars were all left loose so I pushed in the pipe as much as I could twisting to a different setting then tightened up all the collars and the leak so far has stopped so good news apart from the hole in the ceiling!
However I have now cut yet another hole in the other room to find where something else was leaking from the airing cupbouard joints under it but when exposed nothing was leaking suggesting it only leaks and certain times? The 22mm mains pipe is under there with a T going off elsewhere but all seem dry now?
My santon cylinder has some sort of Santon 22mm inlet pressure valve before it with 6 bar knob on top and a plastic cone under it which is dripping very slightly athough I keep a drip tray under that? Its got an allen key attached to its side as if something is adjustable? If I turn the 6 bar knob it flows off some water to the drain ok but only turns one way?
Any idea what this device is and why its dripping at its base? Is it a mains pressure relief valve and does it need replacing if dripping or some adjustment? Expert only job i presume due to mains pressure system?

 

[Agile]

It is a pressure reducing valve and should only be touched by someone who holds a Certificate for unvented cyinders. Its recommnded they are serviced annually!

Tony