Fixing a Dripping Faucet: How to Replace the Cartridge

A single-handle faucet that drips, feels stiff to turn, or has become hard to control for temperature is almost always suffering from a worn-out cartridge -- the small internal part that controls water flow and mixing. It's a fixable, inexpensive repair, though it's a notch more involved than most of the other jobs in this guide, so it's worth being honest with yourself about whether it's the right one to tackle alone.

Signs you need a new cartridge

• A steady drip from the spout even when the handle is fully off
• The handle feels stiff, gritty, or harder to move than it used to
• Water temperature swings unexpectedly or is hard to dial in
• Water leaks out around the base of the handle itself

What's causing it

The rubber seals inside a cartridge wear down with years of use, and mineral deposits from hard water -- common in many parts of Ontario -- speed that up. Occasionally the cartridge itself cracks, or the valve seat underneath it gets damaged.

How to do it yourself

• Turn off both the hot and cold shutoff valves under the sink, and open the faucet to release any pressure -- confirm no water comes out before continuing
• Plug the drain first, so no small screws or clips can fall down it
• Take a photo of the handle and trim pieces before removing anything, so you remember the order they came off in
• Remove the decorative cap, then the screw underneath it, then lift the handle and trim off, keeping the pieces in order
• Note the faucet's brand -- if you're not sure which cartridge it needs, bring the old one to a hardware or plumbing supply store rather than guessing from a photo
• Remove the retaining clip or nut holding the cartridge in place, note which way it's facing, and pull it straight out
• Clean any mineral buildup from inside the valve body gently, without scratching the smooth surfaces the new seals will rest against
• Fit the new cartridge in the exact same orientation as the old one, using a thin film of the plumber's grease the package usually includes
• Reassemble the handle and trim, then turn the water back on slowly and check for leaks and smooth operation

This job means kneeling or sitting on the floor under a sink cabinet for a while, often in a somewhat cramped position. If getting down onto the floor and back up is a struggle, or if your hands have less grip strength or dexterity than they once did for fiddly small parts, this is a very reasonable one to hand to a plumber -- it's typically a quick job for a professional and not a large expense.

Mistakes to avoid

• Buying a cartridge that looks similar but isn't the exact match for your faucet brand and model
• Twisting or straining the supply lines while loosening stiff parts, which can crack them
• Using regular petroleum-based grease instead of plumber's grease, which can damage the rubber seals

When to call a plumber

Call a professional if the old cartridge is seized and won't come out, if the faucet body itself wiggles or moves in the countertop or wall, or if the faucet keeps leaking even after you've confirmed the replacement cartridge is correctly installed. Those situations usually point to a bigger problem than the cartridge alone.