A leaking shower faucet could be a compression faucet or a type of washer-less faucet such as a disc, diaphragm, ball or cartridge faucet. The handles of a compression faucet will turn all the way around and the handles of washer-less faucets will make only a quarter-turn. It requires disassembly to determine what type of washer-less faucet is leaking. Replacing a shower valve cartridge in a cartridge style washer-less faucet is just as simple as replacing a neoprene washer in a compression faucet. When experience is gained with one type of faucet it becomes much easier to repair other types.
Turn off the main water supply to the house. The valves are generally next to the water meter where the water pipes enter the house. Lift up on the faucet lever to drain the lines of water.
Remove the faucet handle by using a hex wrench to unscrew the set screw at the base of and under the lever. Lift off the metal cover under the handle.
Insert a specialised shower socket wrench, available at home improvement stores, into the faucet body and remove the locking nut by turning it counterclockwise.
Pull out the cartridge by lifting it straight out of the faucet body with a pair of pliers. If it is stuck, apply gentle pressure.
Replace the old cartridge with the exact same type from the home improvement store by aligning the holes in the cartridge with those in the faucet body and reinserting it.
Schedule the repair project at a time that the family will not need running water for two hours. Invest in the tools necessary to do the job correctly. This will save time, energy and money over the long term.
Never use excessive force when working on plumbing fixtures as costly damage can result.