I had a problem with our showere where the unit continued to run after it had been switched off or 'pulsed' from time to time of it's own accord. I turned off the power to the shower ( I could still use it as a normal shower) and then changed the micro swich that controls the power to the pump. A new one just fits right in. If your problem sounds similar it could be this. Aqualisa were very helpful in identifying this.
DIY
December 2008