The single shower faucet handle makes a grinding noise when you turn it or it won't turn at all. The hot water is barely hot or there is none, or the water is not being diverted to the shower head. All of these problems are caused by a defective valve cartridge in your shower faucet. The solution is to disassemble the faucet, remove the valve cartridge, and install new replacement parts for your specific shower faucet.
Turn off the main water supply valve outside your house. Open the shower faucet to drain the water lines. Cover the shower floor and drain completely with towels to protect the surface and to keep from losing the parts down the drain.
Remove the diverter handle by removing the screw under the handle with an Allen wrench then lift off the handle. Remove the button from the top of the Acrylic or older metal handle to expose the handle screw. Pry off the button with a screwdriver or unscrew a threaded button with pliers then remove the button. Remove the handle screw with a screwdriver then lift off the handle. Note: There may be a limit stop, handle adaptor, washer or additional parts behind the handle that are removed by pulling the parts straight out.
Use a screwdriver to remove the screws from the front of the escutcheon (wall plate) then lift it from the shower wall. If no screws are present, unscrew the threaded sleeve (turning counter-clockwise) that holds the escutcheon to the wall.
Remove the retaining ring by unscrewing it counter-clockwise by hand or with an adjustable wrench (depending on the faucet). Remove the retaining clip from a Moen faucet with needle nose pliers by gripping the metal lip on the front top of the valve and pulling up. Remove the screws from the gasket (on Kohler faucets) that secures the valve using a screwdriver. Pull the valve and the cartridge out of the faucet. Use a towel to clean up escaping water from the faucet.
Insert the new cartridge into the faucet. Install the new valve assembly making sure the mark indicating top is turned upward. Note: Read the manufacturer's instruction included with the new parts for correct installation of the valve assembly. Remove the towels from the shower floor. Turn the main water supply on.
A Moen valve cartridge is a single piece. Included with the Moen repair kit is a plastic removal tool that is inserted on the valve cartridge and twisted back and forth with pliers until the valve cartridge is loose enough to remove.
Remove corrosion from the faucet using a wire brush or chemicals before installing the replacement parts.