Hi Paul,
My shower had the same problem and eventually the on/off control stopped working too. The problems are linked and it means that there is a little D shaped piece in the controls that has been fitted the wrong way round. If you don't get it corrected then eventually the piece that drives the on/off will split and you will also get the other problem. I can't explain any better as I didn't install or repair it, however, I know this because the Triton engineer has been out and fixed it this morning. I would suggest you get in touch with Triton if it is still under guarantee.
Chris
May 2011
Automatic Answer
While you wait for answers, we may have found some information which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix baths and showers.