I should be a bit more specific about the microswitch and why it causes the problem. The microswitch is a tiny switch operated by a very light touch to make the inner contacts make and break. When you turn the shower on, a cam (or raised lobe) causes the contacts to make and so turn the pump on. When you turn the shower off the reverse happens, the contacts break and stop the pump. Pump run on means the contacts are sticking together regardless of the position of the control knob. The microswitch cannot be dismantled and the only cure is replacement of the microswitch/rectifier loom assembly. The microswitch is not available as an item. It doesn't take much in the way of debris or wear to make it malfunction. The run on of the pump means that the contacts have become sticky and won't separate.
Denis.H - Folkestone.
February 2010