Help with my Quartz pumped shower working intermittently?

My Quartz Electro-Thermostatic shower with pumped processor has started to play up after 5 years of trouble free showering. When I press the switch it runs for a few seconds and then goes off. This will happen a few times and then usually will then run ok. Any ideas as to what could be wrong as I feel that eventually it will stop running altogether.

jenny frost
May 2010