A single handle shower faucet has one handle for both hot and cold water, rather than the traditional two. These fixtures are typically found in updated, remodeled, or new bathrooms. Repairing a single handle faucet is not entirely different than repairing a double handle faucet. Typically, a leaky faucet is due to a worn out O-ring, a small rubber ring which ensures the seal between your shower cartridge and plumbing is tight. Keep in mind, this will be an ambitious task for someone unfamiliar with the work.
Step 1 - Remove the Fixture
Turn off the water. If you cannot do this from the shower, you will need to locate the water shut off from your home's main plumbing lines. Next, close the shower drain so no parts fall down. If you cannot close it, cover it with a towel or cloth. Most faucets have a plastic or metal faceplate that needs to be removed. Pop this off with a knife or screwdriver to expose a small screw. Remove this screw, and carefully set the pieces aside. You may also have to remove the faceplate around your fixture. Simply pop this piece off the wall. If it is kept in place by caulking, carefully remove it.
Step 2 - Remove the Cartridge
The cartridge is the piece of metal work you see sticking out of the exposed fixture. In a single handle shower faucet, you will likely see the hot and cold water shut offs on either side of this cartridge. They are small screws that can be tightened with a flat-head screwdriver. There will be a nut or pin holding the cartridge tightly in place. Remove this with the pliers by turning the nut or popping off the pin. Again, set this aside carefully. Using your pliers, begin to slowly pull the cartridge out of the wall. It should come out easily but move slowly to avoid damage.
TIP: There are also other types of single-handle faucets, like Delta, that have a different type of valve. They employ a ported ball that moves over two spring-loaded washers. To repair these you can buy a kit that replaces all the internal parts. After removing the handle, use caution. When you unscrew the large cap underneath it usually falls apart in your hands. You may have to use needle-nose pliers to remove the two washers and springs in the back of the faucet. Replace all the parts that came in the kit. Don’t forget to use some faucet grease lightly on the parts, and put it back together.
Step 3 - Replace the O-Ring
After removing it, you may see the cartridge is mildewed or damaged, so take this opportunity to clean the cartridge under running water. If it is damaged beyond repair, you should replace the entire thing. Otherwise, simply remove the small rubber O-ring. You can take this O-ring to your hardware store to locate an appropriate replacement. Replacing the tired O-ring with the new one should repair most single handle shower faucet leaks.
TIP: When putting faucets back together, a little faucet grease will help prolong the life of the parts. Lightly apply it to O-rings, washers, and cartridges.
Step 4 - Reassemble
Complete the steps in reverse to reassemble the fixture. This is a good opportunity to clean any soap scum or mildew off of your shower fixture as well. If you sliced the caulking to remove the faceplate, re-caulk this piece, and once the piece is back together, test your work. Turn on the hot and cold water independently to assure there are no leaks.