i had the same problem with my mixer shower ,you cannot repair the thermostatic cartridge ,it has to be replaced by triton ,they are the only stockist of the cartridge ,no one else will stock this item and they will only order from them if they get it for you.it is a simple job to replace , usually a cap that flips off which will give access to a screw holding the knob on ,once the knob is removed removed it will reveal a brass thermostatic cartridge wich is held in place by a grub screw ,once the grub screw is removed usually with a allen key the cartridge can be pulled out with a twist ,check for obvious damage ie rubber o rings worn badly broken etc or other such damage ,if you find that its something simple try replacing the worn /damaged part before buying the cartridge,unfortunatly there are no serviceable parts inside the cartridge and attempting to open one would probably render it useless, when you replace the new cartridge ensure you align the red mark on the cartridge with the 38 degrees marker i hope this has been of help
allan, February 2009
