Sounds like the microswitch behind the control knob. They give up after a time usually failing to the closed position so when you turn the water off the pump keeps running. You need the assembly called the microswitch and rectifier loom assembly. The microswitch is not available separately. As you have not given a shower model number you will have to match the description to your model from a parts list which can be found on the Aqualisa parts site.
Denis.H- Folkestone., February 2010
