We've got the same problem with our shower. We've got this one http://www.aqualisa.co.uk/parts-store/Controls/Aquarian-exposed-thermostatic-and-manual-mixer-valve2/. According to a bit of googling, and confirmed by a plumber, we need a new cartridge (the bit in the the main body of the shower, with the controls either end). There's two types-thermostatic and manual. When you take the 'aqualisa' badge off the body of the shower, unscrew the screw behind it. The top cover will come off and there'll be a model number. If it starts 'm' it's a manual cartridge. We bought ours for £64 inc delivery. Not sure if that helps? Haven't a clue how to actually replace it though (hoping it'll come with instructions!!). I know we'll have to drain the tank-there's no way of isolating just the shower, so we'll have to turn the mains off.
Nic, January 2010
