I know but the short story is that the initial shower was plumbed in correctly by the initial plumber BUT he’d made a bit of a bodge in access ie nightmare should it go wrong
Which 3 years later it did ( dripping head)
Went through bristan
1 Reccd I clean cartridge
2 replace cartridge
3 replace valves
Did all above but not resolved – fault was a crack in body of shower.
Bristan engineer visited to tell us yep body is leaking mate..
Bristan replaced but would not fit as tiles needed removing etc
Enter my plumber.. Who had a mare, removing old shower because of tiles etc