Repair a faucet that does not turn off by determining what type of faucet it is and replacing worn parts. Two-handled faucets are often compression washers, which wear and require replacement, while others have a cartridge that is repaired by replacing O-rings. Single-handle faucets use a cartridge or ball valve.
Begin by turning the valves under the sink counterclockwise to shut off the water. Remove the faucet handle and retaining nut, and use distilled white vinegar to clean parts and remove calcium scale. Compression-style faucets have a rubber washer at the bottom of the brass stem. Remove the retaining screw, and pry the washer from the stem. Replace it with a new washer of the same size. Reverse the steps to reassemble the faucet.
Ball-type faucet assemblies have numerous parts. The easiest way to repair these units is to purchase and install a complete replacement kit. This prevents the faucet from continuing to leak due to an imperfect repair process. When repairing cartridge-type faucets, owners have the option of replacing the entire cartridge, although replacing the O-rings alone is less expensive. When replacing the cartridge, the replacement must be the same length and have the same stem type as the old one.