In message
ilgate.org, Grumpy
owd man writes

0.5 and 1 bar when cold. If the valve drips even when cold replace it. If
it drips when hot then check the pressure vessel pressure or if the
diaphragm is holed replace it.


Ah!, I have not really explained it very well.
the water is coming from a pipe which runs to the outside of the
property if this make any difference. The drip is not internal

Pressure relief valve leaking ?

find it, open it so it gives a good squirt

there might be some crud which is preventing it from seating properly

else, it's a drain down and replace it


--
geoff