Whilst the shower was in use the water flow stopped, there was no change in the sound from the unit and everything seem to be unchanged but the water flow has stopped.

Andy, November 2010

Probably the solenoid valve.
Solenoid valve comes as part of an assembly but you can buy it separately - saves a few quid.
You need to ease the duffer off the assembly with a screwdriver and fit the new one.
You'll get the assembly part number from the installation instructions - looking for the assembly on the web should lead you to a part number for the valve itself.
Shouldn't have to turn the water off but certainly the electricity.

Gordon, November 2010