What It Is
A faucet cartridge is the self-contained valve assembly inside a cartridge-style faucet that controls both water flow and temperature. It sits inside the faucet body, connects to the handle above and the water supply ports below. When the handle moves, it rotates or lifts the cartridge to open and direct water from hot, cold, or both supply lines to the spout. When a cartridge wears out, the internal seals fail and the faucet drips even with the handle fully off.
What It Does
A faucet cartridge replaces the older system of individual rubber washers and seats with a single replaceable unit that handles everything at once. The cartridge contains ceramic discs or rubber seals arranged so that turning the handle aligns or misaligns the flow ports - opening allows water through, closing blocks it. Single-handle faucets use one cartridge; two-handle faucets use one cartridge per handle (a hot cartridge and a cold cartridge).
The advantage of the cartridge design is serviceability. When a faucet drips, you replace the cartridge - a task that takes about 15-30 minutes once you have the correct replacement part - rather than grinding down valve seats and replacing individual O-rings. Cartridges are faucet-brand-specific, so matching the brand and model matters.
Hard water deposits mineral scale on cartridge components over time, which can make the handle stiff or cause the cartridge to stick in a partially open position. This is more common in areas where water has high mineral content.
Where It Is Located
Inside the faucet body, directly under or behind the handle. On a standard sink faucet, removing the decorative cap on the handle, unscrewing the handle screw, and pulling the handle off exposes a retaining nut or clip holding the cartridge in place. The cartridge pulls straight out or lifts free once the retaining mechanism is released.
How It Works
In a single-handle cartridge faucet, the handle connects to a stem that passes into the cartridge. Lifting the handle opens the flow ports; rotating left or right adjusts the hot/cold mix by shifting the cartridge's alignment relative to the hot and cold inlet ports in the faucet body. The ceramic discs inside the cartridge press tightly together when closed - the hardness and precision of ceramic makes this a long-lasting seal. Rubber-seal cartridges work similarly but rely on O-rings that can dry out or wear faster.
Common Problems or Signs of Failure
- Faucet drips from the spout with the handle fully closed
- Handle is stiff and hard to turn - mineral scale on the cartridge or inside the faucet body
- Temperature control is off - water is hotter or colder than the handle position indicates
- Leak from under the handle or at the base of the faucet body - cartridge O-rings are failing
- Handle spins freely without controlling water - cartridge is not engaging the handle mechanism
Can a Homeowner Check It?
- Note the faucet brand and model before purchasing a replacement - cartridges are not universal
- Turn off the supply valves under the sink before any disassembly
- Remove the handle and note the cartridge orientation before pulling it out - reinstalling it rotated 180 degrees will reverse hot and cold
- Compare the old cartridge to the new one before installation to confirm it is the correct part
When to Call a Plumber
If the faucet body itself is corroded, if the cartridge seat is damaged, or if you are not confident identifying the correct cartridge for your faucet model, a plumber can handle the diagnosis and replacement. It is also worth calling if the drip is from a faucet that has already had a cartridge replaced recently - that can indicate the water pressure is too high and is accelerating wear on components.
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