Water flows into the faucet through separate lines for hot and cold water. The temperature is regulated by the cartridge that sits flush against the diverter valve. The cartridge has external O rings that slide against the surface of the valve assembly when the diverter handle is turned. When the diverter handle is engaged, the diverter redirects the water flow from the tub spout to the showerhead. Defective parts and broken O rings can cause the faucet to leak, stop the flow of water to the shower head or inhibit the movement of the diverter handle.
Locate the main shutoff valve to the water supply of your home and turn the water off. Open the faucet all the way to release line pressure and drain the water from
Remove the diverter handle. Some older metal and Acrylic faucet handles have a decorative button on the top of the handle. Use a small screwdriver to gently pry the button off to avoid damage. If the button is threaded, use a wrench to unscrew the button. Use a screwdriver to remove the screw from the handle then pull the handle off. On some faucet models there may be a handle adaptor and washer behind the handle.
Remove the escutcheon, which is the decorative trim attached to the shower wall. If the escutcheon has visible screws, use a screwdriver to remove the screws then lift the escutcheon from the wall. If there is a threaded sleeve behind the handle, unscrew the sleeve by hand, then pull the escutcheon off the wall. (The threaded sleeve may have a washer.)
The valve assembly is secured to the faucet by a flange or gasket and screws. Use a screwdriver to remove the screws then slide the valve assembly straight out of the faucet. Directly behind the valve assembly is the cartridge, which is easily identified by the two chambers in the front. Reach in and pull the cartridge straight out with your hand. Use a toothbrush or wire brush to clean any areas of corrosion from the faucet.
Install the replacement cartridge by sliding it into the faucet. Insert the valve assembly making sure the mark indicating "top" is facing up to ensure hot water will be on the left and cold water will be on the right. Replace and tighten the screws on the gasket or flange to secure the valve assembly. Assemble the faucet, uncover the drain, and turn the water supply back on to test the faucet.
Expect a gush of water when you pull the valve assembly out of the faucet. Keep a towel handy to soak up the water and keep it from running down the inside of the wall. The leak may be caused by the valve assembly, the cartridge or both. To ensure a shower that works impeccably, replace both the valve assembly and the cartridge at the same time.
Shower diverters work the same way regardless of the model or manufacturer. Allow for slight differences in parts and how they are removed.