You'd need a multimeter to find the exact problem, but given the complexity of some showers, its too complex for us to talk through.
Please call an electrician, or seek a replacement shower, same rating (may be cheaper).
A year is quite a short life for an electric shower, but its not unheard of. I've had mine about 6 years now, used 2-3 times a day. We've been lucky I guess.
Just try something for my own curiosity: Turn both the "heat settings" right to their max, the water will barely trickle out, see if its vaguely warm. If it is, an element is shot. Theres 2, sealed into the boiler. You'd need a new boiler (the big copper bit), cheaper to get a new shower.