Yes!

If you have problems with an Excel then it's best just to replace the cartridge, however it is probably worth stripping the cartridge out and checking that the inlet filters are clean, before buying a new cartridge.

To replace the cartridge Pre 2003 units

Turn off hot and cold water supply

Pull front temperature knob off The rest of the knob assy. just unclips

Remove 4 screws that hold cartridge into body

Pull old cartridge forward shouldn't be too tight

Set new cartridge for High/Low pressure (instructions with cartridge)

Slip new cartridge into place remember to check that the new seals are all in place (and don't drop out as you push back)

Tighten screws be careful not to over tighten

Refit knobs.

Turn on water and test. (Occasionally you will have to reset the cartridge temperature, instructions with cartridge)

Easy peasy!!!!

Cartridge Mira 903.33 This cartridge supersedes the previous high and low pressure versions

Link to cartridge

http://www.showerdoc.com/shower-spares/mira/MIRA-903-33-Cartridge-Assembly-(Up-To-2003---Black)-Comes-with-seals