What a Faucet Cartridge Does and Why You Replace It

A cartridge is the part inside your faucet handle that controls water flow and temperature. When you turn the handle, the cartridge moves to open and close the water passages. Over time, mineral buildup and wear cause cartridges to stick, leak, or fail to shut off completely. Replacing the cartridge is faster and cheaper than replacing the entire faucet, and you can do it yourself in 30 to 45 minutes with basic tools.

The cartridge sits hidden inside the faucet body, so you won't see it until you take the handle apart. Most bathroom faucets use one of two cartridge types: a single-handle cartridge (one handle controls both flow and temperature) or a two-handle cartridge (separate handles for hot and cold). Identifying which type you have is the first step, because cartridges are not interchangeable between brands.

Key Takeaways

  • Turn off the water supply under the sink before you start, and test that the water is off by turning the handle.
  • Remove the handle by prying off the cap with a flathead screwdriver, then unscrew the handle screw underneath.
  • Pull out the old cartridge using a cartridge puller tool (rented or bought for $10 to $30) or needle-nose pliers if the cartridge is not stuck.
  • Install the new cartridge by sliding it straight in, making sure the alignment notch matches the slot in the faucet body.
  • Reassemble the handle and test for leaks before you turn the water back on fully.

Gather Your Tools and Identify Your Cartridge Type

You will need a flathead screwdriver, needle-nose pliers or a cartridge puller, an adjustable wrench, and a bucket or towel to catch water. A cartridge puller is a specialized tool that grips the cartridge stem and pulls it straight out without damaging the faucet body. You can rent one from a hardware store for $5 to $10 or buy one for $15 to $30. If the cartridge is not stuck, needle-nose pliers often work instead.

Before you buy a replacement cartridge, you need to know the brand and model of your faucet. Look under the sink or on the faucet body itself for a brand name—common ones are Moen, Delta, Kohler, and Pfister. Write down the brand and any model numbers you find. Take a photo of the faucet and bring it to the hardware store, or search online for "[brand] cartridge replacement" to find the exact part number. Cartridges cost $15 to $50 depending on the brand.

Turn Off the Water and Remove the Handle

Locate the shut-off valves under the sink—one for hot water and one for cold. Turn both clockwise until they stop. If you have a single-handle faucet, you may have one valve that controls both. Turn the faucet handle on to release any remaining water pressure, then turn it off. Place a bucket under the faucet to catch drips.

Use a flathead screwdriver to pry off the decorative cap on top of the handle. The cap usually sits flush with the handle and pops off with gentle pressure. Underneath, you will see a screw. Unscrew it by turning counterclockwise with a screwdriver (or hex wrench if the screw is hexagonal). Keep the screw in a small cup so you do not lose it. Pull the handle straight up and off the faucet body.

Remove the Cartridge Stem and Old Cartridge

Under the handle, you will see a collar or nut that holds the cartridge in place. Use an adjustable wrench to turn it counterclockwise and remove it. Some faucets have a set screw instead—unscrew that first. Once the collar is off, you can see the cartridge stem, which looks like a small cylinder with a flat or notched top.

If the cartridge pulls out easily by hand, grip the stem and pull straight up. If it is stuck, use a cartridge puller: thread it onto the cartridge stem, then turn the handle clockwise to pull the cartridge up. Do not twist or rock the cartridge side to side, because that can damage the faucet body. Once the old cartridge is out, set it aside. You may see mineral deposits or debris inside the faucet body—wipe these out with a clean cloth.

Install the New Cartridge and Reassemble

Before you insert the new cartridge, check the alignment notch on the cartridge stem and the slot in the faucet body. These must line up so the cartridge sits in the correct position. Slide the new cartridge straight down into the faucet body, making sure the notch and slot align. Push it down until it sits flush with the faucet body. Do not force it—if it does not slide in smoothly, remove it and check the alignment again.

Replace the collar or nut by turning it clockwise with the wrench until it is snug. Do not overtighten, because that can crack the cartridge. Reinstall the handle screw and tighten it. Pop the decorative cap back on top. Turn the water shut-off valves counterclockwise to turn the water back on. Turn the faucet handle on and let water run for 10 to 15 seconds to flush out air from the lines.

Test for Leaks and Adjust Water Temperature

Check under the sink for drips around the faucet body and the shut-off valves. A small amount of water may drip for a few seconds as air clears from the lines—this is normal. If water continues to drip after 30 seconds, turn the water off and check that the collar is tight. If the faucet still leaks after you tighten the collar, the cartridge may not be seated correctly. Remove it and reinstall it, making sure the alignment notch matches the slot.

Turn the handle to test hot and cold water. If the temperature does not change or the handle is hard to move, the cartridge may be installed backward. This happens when the alignment notch is not positioned correctly. Turn the water off, remove the cartridge, rotate it 180 degrees, and reinstall it. Test again. Once the faucet works smoothly and does not leak, you are done.

Common Mistakes to Avoid

The most common error is forgetting to turn off the water before you start. Water will spray out when you remove the cartridge, and you will have a mess on your hands. Always locate and test the shut-off valves first. Another mistake is buying the wrong cartridge because you did not check the brand and model. Cartridges are not universal—a Moen cartridge will not fit a Delta faucet. Take the old cartridge with you to the store if you are unsure, and the staff can match it for you.

Do not use a cartridge puller on a cartridge that is not stuck—you may damage the faucet body. Try pulling by hand first, and only use the puller if the cartridge does not budge. Finally, do not overtighten the collar when you reinstall it. Hand-tight plus a quarter turn with the wrench is usually enough. Overtightening can crack the new cartridge and cause leaks.

Frequently Asked Questions

How do I know if my cartridge is stuck?

Try pulling the cartridge stem straight up by hand. If it does not move after a gentle pull, it is stuck. Mineral buildup or corrosion usually causes this. Soak the cartridge area with white vinegar for 15 to 20 minutes to dissolve deposits, then try again before using a cartridge puller.

Can I replace just one cartridge if I have a two-handle faucet?

Yes. Each handle has its own cartridge, and you can replace one without touching the other. The hot-water cartridge is usually on the left and the cold-water cartridge on the right, but check your faucet to be sure. You only need to turn off the water supply to the side you are working on if your shut-off valves are separate.

What if water still leaks after I install the new cartridge?

Check that the collar is tight and the cartridge is seated all the way down. If it still leaks, remove the cartridge and inspect the faucet body for debris or damage. Wipe out any mineral deposits with a cloth. Reinstall the cartridge, making sure the alignment notch matches the slot. If leaking continues, the cartridge may be defective—return it and try a replacement.

Do I need to turn off both hot and cold water?

Yes, turn off both shut-off valves under the sink. Even if you are only replacing one cartridge, water can still flow from the other line and create a mess. Some faucets have a single shut-off valve that controls both lines—check your setup before you start.

How long does a new cartridge last?

A quality cartridge typically lasts 10 to 15 years depending on water quality and use. Hard water with high mineral content can shorten the lifespan. If you notice the handle becoming stiff or the faucet leaking again within a few years, the cartridge may be wearing out sooner than expected.