Boiler leak

Bendy_House

I think what gris says is worth trying - I'm not sure that listening out for drips is reliable enough.

Bottom line - you have a leak! And I don't think you can fully discount it being via the cond pipe. (But, sounds like a thorough job on the PRV pipe    )

Mind you, the 'isolating the boiler test' should be a good pointer. It does, of course, need to be fully isolated, so make sure the valve turn through a full 90o.