Could anyone tell me if this is wrong install.

Had a leak (showing from tundish) when hot water was on and had a plumber out to see if they could sort it, PRV was required and he would need to order it, came back a few days later and said that was wrong size of pipe, it should have been 22mm rather than the 15mm and probably wouldn't be covered by my cover agreement.
He drained the white vessel and tried to recharge it but turns out that the diaphragm was faulty and couldn't get more than 3 bar, phoned around a few places and couldn't get one that day, put the vessel back on that stopped the leak (for now).
Now i've been billed as according to them it is wrongly installed and not covered as the parts are obsolete which i am disputing. I moved in to the house in 2011 as it was a new build and have all the paperwork for the cylander and it came with a 15/22mm tundish, so was it wrongly installed or are the company wrong for this.
cheers.

 

The bits I can see look fine, and parts are still very much available - expansion vessel should be on the shelf at most plumbers merchants, and the safety control group available next day

 

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