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.
Extract the valve cartridge from the shower valve housing by turning the extraction tool's handle clockwise until the valve cartridge is free.
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.
Release the valve cartridge retention ring using snap ring pliers to spread the ring and slip it off the valve's control post.
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.
Turn the main water supply valve on to restore the water supply to the shower valve.
Install the new valve seals by stretching them over the ends of the cartridge and into the seal notches near each end.