I have a old sirrus concealed thermostatic shower over the bath that leaked from behind the wall, dripping all the way to the ceiling below. The leak was constant even if the shower was turned off. It seemed to be from the cartridge hidden behind the tiles. As the parts are too old and out of production. I had to put in a new shower. The plumber installed a Bristan recessed single control shower and this took them 5 hours labour (remove the tiles and old valve, put in new tiles). My question is, how easy for this kind of new shower cartridge to become faulty and leak from behind tiles in the future ? Since it is concealed, it is very difficult to detect leak unless you see water from ceiling downstairs. I did ask for an exposed shower, but they said that would involve much more pipe work. I did not go for this expensive solution. Thanks