A single-handle faucet that keeps dripping after you shut it off is one of the most common small repairs in a St. Louis home. The drip usually comes from one of two places: the cartridge inside the faucet body, or the seat that the cartridge presses against. Knowing which part is wearing out keeps you from buying parts you do not need.

Start by Locating the Drip

Before you take anything apart, watch the faucet closely with the handle fully off. A drip from the spout tip that falls straight down usually points to the cartridge or the seat. Water that seeps out around the base of the handle or from under the decorative plate points to a different problem, such as a worn O-ring or a loose packing nut. Those are separate fixes, so note which one you see before you start.

Shut Off the Water First

Turn off the shutoff valves under the sink. If the valves are stiff or do not close fully, write that down, since a valve you cannot close is a problem on its own and should be addressed separately. Open the faucet to drain the remaining water in the lines. Place a towel in the sink basin so small screws and clips do not go down the drain.

Identify the Faucet Type

Single-handle faucets use a few common internal designs. Some use a cartridge that lifts out as one piece. Others use a ball, a disc, or a stem-style mechanism. You only need the general type, not the brand or model. After you remove the handle cap and handle screw, look at what is visible. A cartridge usually has a metal or plastic retaining clip at the top. A ball assembly usually has a slotted cap on top, and a disc design has a ceramic plate that sits under the handle.

Check the Cartridge

Remove the handle, the decorative cap, and the retaining nut or clip, following the order you see them come off. Lift the cartridge straight up rather than pulling it at an angle. Look for mineral crust, grit, or a rubber seal that is cracked or flattened. Compare the cartridge with the opening it came from. If it is hard to pull out or the stem feels rough when you turn it, the cartridge is a likely source of the drip.

Many St. Louis homes have hard water, so mineral deposits on cartridges and seats are common. Light scale can often be cleaned off with a soft brush and a mild vinegar soak, but check any care notes you can find first. Replace the cartridge if the rubber parts are damaged or the body is cracked, because cleaning will not restore a worn seal.

Look at the Seat

The seat is the metal ring at the bottom of the faucet body that the cartridge seals against. Scratches, pits, or built-up mineral rings can keep the cartridge from sealing even when the cartridge itself is new. Some seats unscrew with a seat wrench, while others are fixed in place. If the seat is pitted, you may need a seat wrench or a seat-cutting tool, and a licensed plumber can handle that step if you are not comfortable with it. Do not force a seat that will not turn, because forcing it can damage the faucet body.

Reassemble and Test

Put the parts back in the reverse order you removed them. Apply a light coat of plumber's grease to the O-rings if the old parts or your notes suggest it, and seat the cartridge fully before tightening the clip or nut. Turn the water back on slowly at the shutoff valves, then test the faucet at low and high flow. If the drip continues, confirm that the cartridge is oriented correctly and that the clip sits fully in its groove.

When to Stop and Call for Help

  • The shutoff valves under the sink will not close fully.
  • The faucet body is cracked or the threads are stripped.
  • Water leaks from the base of the faucet after reassembly.
  • The faucet connects to a sprayer hose or a separate hot water unit you do not understand well enough to service safely.

Stopping early is a reasonable choice when any of these show up. Water damage under a sink can get expensive quickly, so a short service call is often the safer path.

Keep a Simple Record

Write down the faucet type, the part you replaced, and the date. If the drip returns within a short time, the seat may be the real issue rather than the cartridge. A short note helps the next person who works on the fixture, including you, and it makes the next decision easier in your St. Louis home.