Sounds like the microswitches are faulty,this is often caused by them getting wet. How old is the shower? A good clue is the control knob. If you just have one knob which you push in to select H/C setting its a MkI. If you have an on/off knob and an independent H/C selector its a MkII They have different types of switching on each model but both play up if they get wet. In my experience leakage inside the unit was often the root cause. Have you noticed any water leaking out of the bottom of the unit or from around the control knob?
David, October 2010
