Some more photos below after tape has been taken off.
I wasn’t home when the work happened, it was my partner. But the engineer did tell me the flue would have to come off to get to the vessel so I assume maybe he did take it off the wall?
Recently had the expansion vessel replaced in my boiler. This is how the boiler engineer left the flue. I’m not an expert by any means, a competent DIYer but this doesn’t look legit to me. what’s people’s thoughts?