If only one faucet runs weak while everything else in the house has normal pressure, the cause is local to that fixture. A clogged aerator, a partly closed shut-off valve under the sink, or a worn cartridge inside the faucet itself account for the large majority of cases — the household water supply is not the problem.
Why it matters that it is only one faucet
Whole-house low pressure points to the supply line, the meter, or the main shut-off. A single weak faucet, with every other tap in the house running normally, rules all of that out immediately — the restriction has to be somewhere between that specific fixture’s shut-off valve and its spout.
Common causes
| Cause | How likely | What to look for |
|---|---|---|
| Clogged aerator | Very common | Mineral scale visible in the small mesh screen at the spout tip |
| Supply valve under the sink not fully open | Common | Valve was left partly closed after a previous repair |
| Worn or scaled cartridge inside the faucet | Common | Pressure has dropped gradually over months, not suddenly |
| Kinked or damaged supply line | Occasional | Flexible line under the sink pinched against the cabinet |
| Debris in the line after nearby plumbing work | Occasional | Started right after a repair elsewhere in the house |
| Corroded galvanized pipe feeding just that fixture | Less common | Older homes with original galvanized plumbing |
How to fix it
- Check the shut-off valve first
Look under the sink and confirm the valve is turned fully open — a valve nudged partly closed during other work is a surprisingly common and completely free fix.
- Clean the aerator
Unscrew it from the tip of the spout, usually by hand or with pliers wrapped in a cloth to avoid scratching it. Soak it in vinegar for 15–20 minutes to dissolve mineral buildup, then rinse and brush out any remaining debris before refitting.
- Test with the aerator removed
Run the tap with the aerator off. If pressure is strong without it, the aerator was the whole problem. If it is still weak, the restriction is further back in the fixture.
- Check the supply line for a kink
Follow the flexible supply line from the valve to the faucet and look for a pinch point, especially if the cabinet is tightly packed.
- Consider the cartridge
If pressure has been declining gradually over a long period and the aerator and valve check out, the internal cartridge may be scaled up or worn — this is a standard, inexpensive part on most faucets.
When to call a plumber
If the aerator, valve and visible supply line all check out but pressure is still weak, have a plumber inspect the fixture’s cartridge and the pipe feeding it — in older homes with galvanized plumbing, internal corrosion narrowing that specific pipe run is a common eventual cause.
Stop and call a qualified appliance technician or electrician if you find scorched or melted wiring, smell burning, see water that has reached electrical components, or if the fault returns immediately after a repair. Never bypass a safety device — thermal fuses, door interlocks and flood switches fail for a reason, and defeating one converts a broken appliance into a fire or flood risk.
