Vaillant VCW GB 242E Over presure valve leaking - when the heating is
off and the pressure is set to 1 bar -

The over pressure 'saftey valve' is leaking slightly .. ie the system
pressure is slowly dropping and the there is a slow 'drip' from the
vent pipe out side ..

I see the valve appears to be part of the boiler - can be un-screwed -
leaving the housing behind ..

Question is ... can it be serviced ? or is it a sealed unit ? if you
unscrew the 'insert' do you also need to remove the housing to
change it ?

Just need a idea before I make a start !

Tnx G ,