Faucet Has Weak Flow
When one faucet has weak flow but the rest of the house is normal, start with local restrictions: the aerator or spray head, partially closed or restricted supply valves/lines, and then the cartridge or internal passages depending on the faucet design. Checking whether hot, cold, or both are weak helps narrow the cause before replacing a cartridge.
- —Clogged aerator screen (mineral buildup from hard water — the most common cause)
- —Failing or partially blocked cartridge inside the faucet
- —Partially closed supply valve under the sink
- —Kinked or restricted supply line
Try This First
Safe, simple steps you can try yourself. If any step feels beyond your comfort level, skip it and continue below.
- 1
Check other fixtures
Run other faucets and the shower. If they have normal flow, the problem is isolated to the one faucet — not a whole-house pressure issue.
- 2
Remove and clean the aerator
Unscrew the aerator from the end of the spout (by hand, or with pliers wrapped in a cloth). Take out the screen and soak it in vinegar for 15 minutes to dissolve mineral buildup. Rinse and reinstall. Note the order of the parts — they must go back in the same sequence.
- 3
Check the supply valves
Under the sink, make sure both hot and cold supply valves are fully open (turn counterclockwise). A partially closed valve restricts flow.
- 4
Test hot vs. cold
If only hot or only cold is weak (not both), the problem is in that supply line or valve — not the faucet itself.
If the problem is resolved
If cleaning the aerator restores full flow, the problem was mineral buildup. Soak the aerator in vinegar every few months to prevent recurrence.
If the problem persists
If cleaning the aerator doesn't help and the supply valves are fully open, the cartridge inside the faucet may be failing. Continue below.
Stop and Call a Plumber If…
- Cleaning the aerator doesn't restore flow — the cartridge may be failing
- Both hot and cold are weak at the same fixture (unusual for aerator alone)
- The faucet is also leaking or hard to turn
- The supply valve under the sink is stuck or won't turn
- ✓Removing and inspecting the cartridge for blockage or wear
- ✓Checking the supply line for kinks or internal restriction
- ✓Testing the supply valve for proper operation
- ✓Replacing the cartridge with the correct part for the faucet brand
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Reviewed by Paul Hall, Owner & Licensed Plumber
The Classic Plumber · Knoxville, TN · License #4268. This guidance is general — an onsite inspection may be required for a confirmed diagnosis.