Hi Assume you have checked the mains circuit breakers ( shower should have its own individual breaker ) might just need re-set if power was interrupted ( pushed up like the others - do you see any red light on the bathroom pull switch or on the actual unit to show power is getting there
Failing a circuit breaker manual re-set the most likely cause is that the heater element has burned out and any competent spark should isolate the power -remove the cover - establish cause
PLEASE PLEASE PLEASE do not let anyone tamper with it if they are not competent to circuit test it afterwards
I would not advocate trying to fix a shower unless I was a qualified electrician and they will probably suggest fitting a new one -- get quotes first
pc6493, November 2009