My guess is that the solenoid valve on the inlet pipe has died. This assembly is held closed by water pressure and power is needed to pull it back to allow water through to the heater coils. These systems are designed not to operate in the absence of water flow for safety reasons. The valve will be fine, it is the electrical coil within the solenoid which is at fault. Disconnect the shower unit from the mains supply and disconnect the solenoid terminals, Its the little cylindrical device immediately to the right to the stabiliser valve (the lower knob). Try a voltmeter across the solenoid and it should register some continuity, if no continuity the coil is fried. Triton will be the best place to get a replacement part.
Answers & Comments
My guess is that the solenoid valve on the inlet pipe has died. This assembly is held closed by water pressure and power is needed to pull it back to allow water through to the heater coils. These systems are designed not to operate in the absence of water flow for safety reasons. The valve will be fine, it is the electrical coil within the solenoid which is at fault. Disconnect the shower unit from the mains supply and disconnect the solenoid terminals, Its the little cylindrical device immediately to the right to the stabiliser valve (the lower knob). Try a voltmeter across the solenoid and it should register some continuity, if no continuity the coil is fried. Triton will be the best place to get a replacement part.