Interesting, I've kept a hold of the previous expansion vessell when it was replaced and found not to be the issue so at least I have the spare part, many thanks for your input I was starting to think I needed a new boiler I'd changed that many parts :)
Hi,
First time poster. We have replaced the pressure release valve, the pressure vessel and the heat exchanger and still experiencing drops on pressure overnight which require a top up to fire the boiler up. No leaks in the system as had thermal imaging survey also no drop of pressure...