A tub faucet diverter is a small flap behind your bathtub faucet handle that determines whether water will flow out of the shower or out of the tub faucet. In a single-handle faucet, you will likely have to push or pull the shower faucet handle to divert water. In a triple-handle tub faucet, the center handle controls the diverter. Separate showers and tubs do not have this feature. Replacing the tub faucet diverter involves accessing the plumbing behind this shower faucet handle.
Step 1 - Remove the Existing Cartridge
First, plug the shower tub to prevent any shower parts from falling down the drain. You can do this by laying a towel over the drain. Next, remove the handle above the shower faucet stem. Remove its screw and pull the handle off. You will need to shut off the water by turning the shut off screws for both hot and cold. Last, remove the nut that holds the cartridge in place. You should do this with soft pliers to avoid stripping the soft copper that usually is used in piping. Using the pliers, pull the cartridge out slowly.
Step 2 - Remove the Faucet Diverter Stem
The diverter stem will be on the back of the cartridge. It is a small plastic flap. You will see a round nut holding the stem in place. Use your pliers to carefully remove the nut. If the nut gets stuck, be careful. Use oil to loosen the nut, and try using a wrench if the nut is stripped. If you damage this system, you will need to replace the cartridge entirely.
Step 3 - Install a New Stem
Take the cartridge to your local hardware store to be certain your replacement stem will fit correctly. Since hardware stores carry multiple stems, you will likely have no problem locating the appropriate new tub faucet diverter stem. The new stem should slide easily onto the same fixture that held the old one. Tighten the nut in place. You should practice fitting the new stem into the cartridge prior to placing the cartridge back into the wall. If you have difficulty getting the new stem to slide into place, consider using a mild lubricant. Again, be careful not to damage the soft metal of the fixture.
Step 4 - Reinstall Cartridge & Test
Reinstall the cartridge using the same method you used to remove it. You can use a small amount of plumbers tape to cover the nut that holds the cartridge in place. This helps ensure a strong seal even with an older cartridge. Remember to turn the screws for the hot and cold water shut off back to "on" prior to replacing the handles. Once everything is back in place, test your work. Turn on both the hot and cold water. Ensure the diverter works in both directions.