A shower faucet holds parts inside the handle that make it function properly. If the faucet leaks or has water flow problems, changing out these parts solves the issue. The main component in a shower faucet today is the cartridge, which contains the two valves for the hot and cold water inlets. Replacing this part is one of the more common shower faucet repairs. To do this, take apart the faucet first. This requires a complete disassembly of the handle and inner parts.
Turn off your water supply by closing the main water valve near the home's water heater.
Remove the handle to the faucet. Locate the small set screw that attaches it to the faucet stem. Most are located on the back of the handle near the base, or on top of the handle under a cover. Remove the cover to get to the screw. Use an Allen wrench or screwdriver to unscrew the screw and slide off the handle.
Remove the handle adapters if your faucet has them, by unscrewing the adapter screws with a screwdriver and pulling them off. Slide off the trim sleeve by unscrewing it and pulling backwards and then remove the retaining nut at the base of the faucet. Some faucets may have a bonnet cap, a small, round, dome-shaped piece under the handle, and a retaining nut instead of a trim sleeve. Unscrew the bonnet and remove it, using a pair of pliers if needed.
Pull out the cartridge by sliding it backward out of the faucet body. Inside the faucet body there may be two rubber seals. Remove these by lifting them out with a screwdriver or the tip of the Allen wrench.
Take off the trim sleeve, the round plate that fits over the shower wall at the base of the faucet by unscrewing the two trim sleeve screws with a screwdriver and pulling off the trim. This gives access to the outside body of the faucet.