If your shower control is leaking or your shower head is dripping then you will need a new cartridge
The way to tell the cartridge you need is to remove the On/Off Control (pulls off) and the Temperature Control (4 screws), and look at the colour of the ring that the screws go into, you do not need to turn the water off until replacing the cartridge itself
On/Off control (white 024604, chrome 024601 or white/gold 024605)
Temperature control (white 024502 or black 024501)
Thermostatic cartridge (grey=standard 022801, pink=multipoint/combi-boiler 022802)includes gasket and screws
note If you have a cartridge with a black ring use the grey one as a direct replacement
Manual cartridge (blue 022804) includes gasket and screws
