Isolate the hot and cold water supplies by means of the integral ball valves accessed underneath the tap spigot. Open the levers to allow residual water to drain. Remove the tap's bottom cover cap using a strap wrench. Using a 12mm hex key remove the thermostatic cartridge cover. Screw in the cartridge removal tool then pull downward to release the cartridge. A replacement cartridge can be fitted in its place. Replace the thermostatic cartridge cover with the 12mm hex key. Replace the tap's bottom cover cap and tighten using the strap wrench. Reopen the hot and cold water supplies.