Your bath faucet has a cartridge behind the handle that controls the flow of water from the shower valve. The handle controls the water by gripping the hex end of the cartridge and turning it. Unfortunately, over time, the hex end of the handle may be worn down by a process called stripping. This may cause grinding when the handle is turned, a loose feeling or a lack of water coming from the shower. If these warning signs are present, you may need to repair the cartridge or replace it completely.
Slightly Worn Cartridge End
Turn the water for the bath off by shutting down the water mains for the bathroom.
Remove the cover, or shield, of the bath faucet handle with a flat head screwdriver to reveal the screw underneath.
Remove the screw holding the handle down with a Philip's head screwdriver.
Pull the handle off of the cartridge behind it.
Inspect the cartridge end to see how worn the head of the cartridge is. Look for a rounding of the cartridge head on a slightly worn head; a badly worn head will have no edges for the handle to grip on to.
Wrap the end of the cartridge twice with a length of plumber's tape to give it a better grip and reinstall the handle.
Turn on the water to the bath and check the functionality of the handle.
Badly Worn Cartridge
Shut off the water and remove the handle as before.
Lift off the retaining clip of the cartridge using a flat head screwdriver. Slide the end of the screwdriver under the clip and pull up.
Place the cartridge puller over the cartridge in the wall and turn the knob at the end of the cartridge puller. Continue turning until it engages the end of the cartridge and the cartridge puller knob is tight; pull the cartridge out from the wall. Turn the knob one full turn using a wrench if the cartridge remains stuck.
Align the cartridge so it fits into the shower valve at the back of the wall. Push the cartridge into the valve as far as it will go.
Reinstall the retaining clip. Reinstall the handle and tighten the handle down with the screw. Replace the screw cover.
Turn on the water and test the faucet.