Why does one faucet have low pressure?
Updated August 2026
When one faucet trickles while the rest of the house runs strong, the culprit is almost always a clogged aerator, the little screened tip that threads onto the spout and catches mineral grit. It is the cheapest fix in plumbing: unscrew it, rinse the sediment out, and flow usually jumps back to normal in five minutes. If a clean aerator does not do it, the restriction is deeper, in the cartridge or the shutoff, and those are covered below.
Causes, most likely first
| Cause | How likely | The fix | Typical cost |
|---|---|---|---|
| Clogged aerator at the spout tip | Most common | Unscrew the aerator, brush out the grit, soak it in vinegar for an hour, and reinstall. | Free |
| Clogged or worn valve cartridge | Common | Sediment or scale in the cartridge chokes flow. Clean it, or drop in a new cartridge. | $15–60 part |
| Partly closed supply shutoff | Common | A stop under the sink that got bumped or was never fully opened starves the faucet. Open it all the way. | Free |
| Kinked or crimped supply line | Occasional | A braided hose bent behind the cabinet restricts flow. Straighten or replace it. | $8–20 |
| Debris from recent plumbing work | Occasional | Solder bits or pipe scale loosened by a repair lodge in the aerator or cartridge. Flush the line with the aerator off. | Free |
| Corroded galvanized supply pipe | Rare | In old homes, rusted galvanized pipe narrows and drops pressure at fixtures on the end of the run. Repipe that section. | $300–1,000+ |
Check these first
- Confirm it is only one faucet. If every fixture is weak, the problem is the main supply or a pressure regulator, not this faucet.
- Test hot and cold separately at the weak faucet. If only the hot side is weak, suspect the water heater or a hot-side cartridge; if both, start at the aerator.
- Unscrew the aerator and turn the faucet on without it. Strong flow with the aerator off means the aerator was the whole problem.
- Reach under the sink and check that both shutoff valves are turned fully counterclockwise (open).
- Look at the braided supply lines for a sharp kink where the cabinet crowds them.
Prevent it next time
Low flow at a fixture is a hard-water problem more than a plumbing failure. Clean the aerator every 6–12 months (more often on well water or above 7 grains of hardness) and the grit never gets a chance to pack solid. Running the whole house through a softener slows scale in aerators and cartridges alike. Those small habits are why a quality faucet routinely lasts 15–20 years before the valve body itself wears out. Our faucet checklist covers the rest.
When to call a pro
Call a plumber when a clean aerator, an open shutoff, and a fresh cartridge still leave the faucet weak, which usually means the restriction is in the supply piping. Expect $100–200 for a diagnostic, $150–350 to replace a faucet or rebuild a valve, and $300–1,000 or more to repipe a corroded galvanized run. If the low pressure showed up across several old fixtures at once, aging pipe is the likely cause and worth a professional look rather than another cartridge.
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Stop chasing symptoms, free for 30 daysFrequently asked questions
Why is only my hot water pressure low at one faucet?
Two usual reasons. Sediment from the water heater can settle on the hot side of the faucet cartridge or in the aerator, choking only the hot flow. And a partly closed hot shutoff under the sink, or a kinked hot supply line, does the same thing to one side. Pull the aerator and test; if hot is still weak with it off, clean or replace the cartridge and confirm the hot stop is fully open before blaming the water heater.
Can a clogged aerator really drop the flow that much?
Yes, and it is the number one cause of a single weak faucet. The aerator screen has openings smaller than a pinhead, so it only takes a little mineral scale or a few flakes of pipe debris to block most of them. Because it is the last thing the water passes through, whatever the pipe carries ends up trapped there. That is why unscrewing and rinsing it is always the first move, and why it fixes the problem far more often than any paid repair.
How do I know if it is the faucet or the whole house?
Run other faucets and check the shower. If every fixture is weak, look at the main: a failing pressure regulator, a half-closed main shutoff, or a clogged whole-house filter, and normal house pressure reads about 40–60 psi on a hose-bib gauge. If only this one faucet is weak while the rest run strong, the problem is local to that fixture, almost always the aerator, the cartridge, or its shutoff valve.