Nope. The only thing I was going to suggest was a larger exp vessel, but they've done that. The reason I was going to suggest this is because a running pressure of 2 bar is really too high, and is not too far from possibly opening the safety release valve. Certainly uncomfortably high, so that's something I'd like sorted regardless of anything else. Since they fitted the larger exp vessel, has there been any improvement in the 'hot' pressure - ie has it become a bit lower, or is it still 2 bar? Anyhoo, one thing I'd like to determine - is there any water being lost out the safety discharge pipe? That should help to identify the cause of the lost pressure. Wrap a small clear poly bag around the pipe outlet using a rubber band or similar, and keep an eye on it.