For me it was one of two things. Firstly my shower head was so blocke dit was beyond beleif. Once cleared the problem still persisted so I check the pcb. There were two components that were very loose on the board (one was the switch). There is an image here which shows the offending items with arrows
http://www.family-burgess.com/temp/images/triton_opal_2_pcb_01.jpg.
I resorted to removing the board and re-soldering said components so that they were in their original position. Problem went away immediately. There's no way I wanted to spend £63 + vat on a new board and I have the benefit of now knowing my soldering is a bit more beefier than some mass produced PCB on a line. Just to add the above worked for me as I am a dab hand at soldering and electronics etc, I wouldn't recommend the above course of action if you don't know what you are doing.
Jason_B
October 2009