mira sport shower not coming on?

My Mira shower has recently developed a fault. When the main power switch is switched on the 3 red lights come on as normal.(high, med, and low power settings).
However when the appropriate button is pressed the 3 lights brighted but no water flow commences. Normally the pushed button light goes green and the other 2 go out.
I dont know if this is a water problem or an electrical one.