On 18:57 9 Apr 2021, Tim+ said:

Pamela wrote:


I had a new one fitted in the external pipework. Should the
failed expansion vessel inside the boiler have been isolated or
perhaps drained?


I can't see that it would be worth the bother. Presumably you
had an external one fitted because changing the internal one was
bothersome.

Tim

That's correct: it was filling and emptying in an erratic way. It's
still in series with the new expansion tank in the water circuit.