Cartridge faucets are the easiest kind of faucet to repair. It only takes about an hour to fix a leaky cartridge filter faucet. Leaky faucets waste water, so fix them as soon as possible.
Gather your materials: Screwdriver, hex wrench, groove-joint pliers, silicone grease, needle-nose pliers, replacement cartridge and replacement O-ring for your brand of faucet. If you can’t remove the old stem with pliers, you'll need a brand-specific stem puller. Take the old parts with you to the store to be sure you get the right brand of replacement parts.
Shut off the water under the sink and turn on the faucet until the water stops running. Drain off the water to prevent a mess.
Remove the retaining screw and lift off the handle.
Use a hex wrench to remove the retaining screw. Set the faucet aside.
Remove the retaining nut under the handle.
Use a screwdriver to remove the nut.
Remove the retaining clip.
Pull out the retaining clip located just beneath the retaining nut.
Remove the plastic retaining caps.
Unscrew the retaining caps by hand.
Remove the spout housing ring.
Unscrew the ring that holds the spout housing the faucet body.
Lift the faucet spout straight up off the housing body.
Set the spout aside. Clean the faucet body to remove any debris using an old toothbrush.
Remove the clip at the top of the cartridge.
Use needle-nose pliers to remove the clip.
Remove the old O-ring.
Use the tip of a screwdriver to slip the old O-ring from its groove and remove it from the housing. Avoid cutting the ring off the housing so that you can take the intact O-ring to the store to get an exact replacement.
Pull the cartridge straight up to remove it.
Use groove-joint pliers to grip the old cartridge and pull it straight up. Be careful not to break or damage either piece. If the pliers won’t work, buy a tool called a stem puller that was made for your brand of faucet.
Clean the faucet and the faucet body to remove debris.
Coat the O-ring with silicone grease.
Use your fingertip to apply a light coating of silicone grease to the new O-ring, and install it in the groove on the faucet body.
Insert a new cartridge (or reattach the old one if it’s still in good shape).
Reinstall the clip on the cartridge, slide the faucet spout on the housing body, and screw on the retaining ring.
Reinstall the plastic nut.
Hand-tighten the nut so that it doesn’t strip.
Reinstall the plastic cap.
Secure it snugly.
Reinstall the retaining nut.
Clip along with the faucet handle.
Turn the water on under the sink to check the temperature. It’s surprisingly easy to get the hot and cold reversed.