Although a number of different valves are used in showers, the cartridge valve perhaps is the most common faucet type for single-handle assemblies. Unlike with two-handle assemblies, whereby one handle controls cold water and another controls hot water, the cartridge valve combines hot and cold water to the desired temperature. For this reason, cartridge valves sometimes are called "mixer" valves. Fortunately, replacement cartridges are comparatively inexpensive and straightforward to install.
Turn off the home's water supply with a water main wrench.
Remove the securing screw from the centre of the valve handle with a screwdriver and pull the handle off of the valve.
Remove the chrome escutcheon plate attached to the wall of the shower. Remove the plate's screws with the screwdriver and lift the plate away from the wall to expose a large bonnet nut that surrounds the cartridge.
Turn the bonnet nut in a counterclockwise direction with an adjustable wrench and remove it.
Pull the old cartridge out of the wall using channel-type pliers.
Insert the new cartridge into the wall. Note that the cartridge features two plastic tabs that must align with two slots cut into its housing within the wall.
Tighten the bonnet nut over the cartridge to secure the cartridge in place.
Position the escutcheon plate over the cartridge, and tighten the plate's screws through the plate and into the shower's wall.
Slide the handle onto the tip of the cartridge and tighten the handle's screw into the centre of the handle.
Turn the water supply on.