It should have been put in with some kind of isolator switch. Maybe a pull cord switch from the ceiling or a nice chunky rocker switch on a wall outside the bathroom. Failing that, it's probably powered from a dedicated circuit breaker in your consumer unit (fusebox). Just turn it off at the isolator or circuit breaker.

As for getting hints what's wrong with it, have a wander round www.showerdoc.com

Eheheh
January 2022