If you're constantly seeing water dripping form the pr pipe then it could be-
faulty pr valve
filling loop passing allowing water into system until it reaches 3bar+ and leaking from pr.
faulty h/ex allowing same prob as above.
if you see water dripping when the heating is on then could be expansion vessel.
this prob would be like:
boiler cold-pressure guage 1 bar-no water from pr
boiler hot (heating on a while) pressure guage 3bar+-water from pr
cold again-1 bar or less and requiring top up.
ideally boiler would be 1 bar cold and rise to 2---2.5 max when heating on.
iain
March 2008