The seals in a shower faucet are small neoprene rubber rings that compress as the valve is adjusted to control the flow of water and subsequently control the hot and cold water mixture that maintains the desired shower temperature. A slow drip or wandering water temperatures can be the first indication that your shower faucet’s valve seal is in need of replacement.
Turn the main water valve off to stop the water supply to the shower valve, then open the shower valve to release any water remaining in the water lines.
Loosen and remove the shower valve handle by removing the retainer screw located under the center cap of the handle. The center cap is easily removed by prying the point of a utility knife blade under the edge. For level-type valve handles, loosen the small set screw at the base of the handle, and pull the handle off the valve's control post.
Release the valve cartridge retention ring using snap ring pliers to spread the ring and slip it off the valve's control post.
Place the cartridge extraction tool over the valve's control post and tighten the tool’s end screw into the end of the post.
Extract the valve cartridge from the shower valve housing by turning the extraction tool's handle clockwise until the valve cartridge is free.
Remove the old rubber seals from the valve cartridge by stretching them over the end of the valve or cutting the seal with a utility knife.
Install the new valve seals by stretching them over the ends of the cartridge and into the seal notches near each end.
Insert the valve cartridge into the shower valve housing, pressing it straight in until it is fully seated. Secure the cartridge retention ring removed in Step 3 using snap ring pliers to spread the ring, slipping it over the valve control post and into its slot against the cartridge.
Reinstall the shower valve control handle removed in Step 2, and secure by tightening the center screw, then snapping the screw cover cap into place. For a lever control handle, position the lever angle as desired and tighten the small set screw at the base of the handle.
Turn the main water supply valve on to restore the water supply to the shower valve.