In order to successfully repair a shower faucet, it is important to get the facts concerning the faucet you will be repairing. There are many types and styles of faucets available, but they mainly fall into two categories: washer (compression) and the washer less types.
There are a number of reasons a shower faucet might leak:
Loose or worn packing
Worn washer
Worn valve seat
worn o-rings
sediment build up on disc type faucet
worn seals on disc type faucet
To begin repairing your faucet, first turn off the water supply. Open the valve to make sure all water is drained down. Next, remove the faucet. You should then check for mineral deposits. If there is a buildup on the faucet assembly, you can soak the assembly parts in white vinegar or purchase a solution designed specifically to dissolve lime (often needed to remove heavy buildup).
Next, unscrew the retaining nut with a shower stem socket tool (available at most hardware stores).
To remove the cartridge, just grasp the end with a pair of pliers and pull straight out. If the hole is too small, you can enlarge it with a screwdriver and hammer.
After the faucet is removed and soaking (if necessary), check for caulking around the escutcheon plate. To remove the left behind caulking, simply use a plastic putty knife, being careful not to damage the surface.
Next, peel off the o-ring. Just slip it from its grove and peel from the housing. Keep the o-ring whole (do not cut) so you can easily find an exact replacement at the hardware store. If you are not able to peel it off, you can play it off with a screwdriver. Make sure that the o-ring groove is free of any buildup or lime deposits.
The next step is to apply silicone grease to the new o-ring. Slide the o-ring over the cartridge, seating it into the o-ring grove. Reassemble the faucet. Turn the water back on and test for leaks.
Replace the escutcheon plate and seal around it with bathtub caulking.
Below is a list of supplies you will need to make a successful shower faucet repair:
O-ring
cartridge replacement kit
silicone grease
white vinegar or lime dissolving solution
caulking (water proof - clear dry)
You will also need a screwdriver, a plastic putty knife, shower stem socket kit, pliers, and a utility knife. You may also need a flashlight.
After completing your shower faucet repair and checking for leaks, your faucet should be good as new.