A single-handle faucet has washers called O-rings, located around the spout area at the base of the fixture. Changing these washers requires removal of the handle and cartridge. The repair fixes leaks occurring from the base of the faucet and unseen leaks in the shower wall. Allow ample time to perform the repair correctly.
Shut off the water valves to the faucet. Find them behind the shower wall, accessible via a panel door in the wall. If there is no access panel, close the home's main water valve.
Remove the faucet's handle by loosening the set screw at the base of the handle with an Allen wrench, then sliding it off. Take off the retaining clip or the bonnet (dome-shaped piece) to expose the cartridge. Remove the cartridge by pulling it out.
Remove the trim screws with a screwdriver and slide them out. Take off the trim plate to expose the entire faucet assembly. Slide the O-ring washers off the base of the fixture and replace them with new O-rings.
Replace the trim and cartridge. Install a new cartridge to replace the valves inside of the cartridge. Replace the bonnet or retaining clip and reinstall the handle.