If your shower control is leaking, the shower head is dripping or you have lost control of the temperature then you will need a new cartridge
Cartridge Body, choose 164310 thermostatic (black band) or 164312 manual (blue band). (If it has AQUARIAN on the On/Off control it is thermostatic). Also thermostatic cartridges have a serial number beginning 'T' whereas Manual ones begin 'M'
On/off control: 164320 white, 164321 chrome or 164322 gold
Temperature control: 164325 white, 164326 chrome or 164327 gold
Front Shroud: 164315 white, 163316 chrome * or 164317 gold * chrome shroud is no longer available either choose white or replace with current Aquarian model