How to Replace a Leaking Bathroom Faucet Cartridge

Faucets are the hardest-working fixtures in your home, and eventually, the internal seal—the cartridge—will succumb to mineral buildup or simple wear. When you see a persistent drip or feel the handle struggling to turn, it is time for a cartridge swap. It is a precise task, but well within the reach of anyone willing to work methodically. Getting this right means having the exact replacement part in hand before you take anything apart. If you rush into this without the right cartridge, you will end up with a dismantled sink and a trip to the hardware store that leaves you without running water. Follow these steps, and you can restore a smooth, leak-free flow in an afternoon.

Stop the water supply. Locate the isolation valves under the sink and turn them clockwise until tight. Open the faucet handle to drain any remaining water and confirm the lines are clear.
Expose the set screw. Pry off the decorative cap on the handle to reveal the set screw. Use an Allen wrench or screwdriver to loosen the screw and pull the handle straight off the stem.
Access the cartridge. Remove any bonnet nut or decorative trim sleeve protecting the cartridge. Use an adjustable wrench to carefully unscrew the retaining nut holding the cartridge in place.
Remove the old cartridge. Pull the old cartridge straight up and out of the faucet body using pliers if necessary. Note the orientation of the cartridge, as it must go back in the same way.
Clear mineral deposits. Use a soft brush or cloth to clean any mineral deposits or debris from the inside of the faucet body. A smooth, clean surface ensures the new O-rings seat properly.
Seat the new cartridge. Slide the new cartridge into the body, aligning the notches or tabs with the slots in the faucet housing. Tighten the retaining nut securely but do not overtighten.
Verify the fix works. Reattach the handle, open the water valves slowly, and run the faucet to flush air from the line. Check for leaks around the base of the handle.