My boiler, which I think is not untypical, has a filling loop with 1/2" loosely retained nuts at the end, superficially like a tap connector. But instead of a flat for a washer at the interface to the tap it has a boss that fits inside the bore of the 1/2" special tap with an O-ring around it which fits in the polished internal bore of the tap. One of the taps is leaking, and I can't find the official part for my somewhat obsolescent Firebird Combi.
Does anyone know of a name for this type of connector, especially as applied to the tap part?