vaillant water pressure problem

[adeybaby]

A friend (honest) has a vaillant vc gb 112eh or vc gb 142eh(not sure which instruction manual covers both) and after removing and re connecting a radiator and bleeding it he has a problem where the water pressure keeps dropping (below 1bar) . he refills and after a day or 2 it needs refilling again .
no leeks at the radiator but pipe going to outside is dripping, any ideas
as to the problem and the cure

 

[kevplumb]

prv needs replacing

is the pressure rising above 3 when running

 

[adeybaby]

pressure doesn't go above 3 just drops of
if the prv is faulty shoul it be leeking or is that whats coming out the pipe on the outside wall

 

[kevplumb]

it's what's coming out of the pipe

 

[adeybaby]

thx where do i get one and is it easy to fit