Low pressure at bathroom sink only

Quick Answer:

If only the bathroom sink has weak flow, start with the local controls: make sure the angle stops under the sink are fully open, remove and rinse the aerator, and inspect the flexible supply line for internal collapse. If those checks don’t help, remove the cartridge and flush the valve body carefully to clear debris.

Why This Happens

When low pressure affects a single fixture, the cause is almost always local rather than a house-wide supply problem. Common causes include partially closed angle stops, a clogged aerator, a kinked or internally collapsed flex line, or debris trapped in the faucet cartridge or valve body. These are usually easier to diagnose and fix than whole-house pressure issues. For similar but different problems elsewhere on the property, see Outdoor spigot has weak pressure and for issues that follow adding filtration, check Low pressure after installing water filter.

Step-by-Step What to Do

1. Confirm it’s only this sink

• Turn on another faucet in the house briefly. If those fixtures have normal pressure, focus on the bathroom sink.

2. Open the angle stops fully

• Locate the two small shutoff valves under the sink (angle stops).
• Turn each counterclockwise until they stop. Some stops are quarter-turn; others turn fully. Make sure they are fully open.
• If a stop won’t turn, don’t force it—move to the next steps or shut the main water off before attempting further repairs.

3. Remove and rinse the aerator

• Unscrew the aerator from the spout by hand or with a cloth-wrapped pliers to protect the finish.
• Rinse the screens and small parts under running water. Use a soft brush to remove mineral scale.
• Reassemble and test the flow.

4. Check the flex supply line for internal collapse

• Shut the angle stops off, place a bucket under the connection, and disconnect the flex line from the valve or faucet.
• Look through the line for obstructions and bend it gently to see if it kinks or collapses internally. If it’s damaged or looks flattened inside, replace it.
• Reconnect and open the stops to test. Replace the line if flow improves when bypassing it.

5. Remove the cartridge and flush the valve body carefully

• Turn the angle stops off and open the faucet to depressurize the lines.
• Remove the handle and trim to access the cartridge or valve stem per the faucet design. Keep track of small parts.
• With the cartridge removed, briefly open the angle stops to flush water through the valve body and clear debris—do this over a bucket and be ready for a short, dirty spray.
• Inspect the cartridge for debris or damage and clean or replace it as needed, then reassemble and test.
• If you’re unsure which cartridge you have or how to reassemble the faucet, take photos during disassembly or stop and call a pro.

What Not to Do

• Don’t overtighten the aerator—stripped threads create leaks and don’t fix clogs.
• Don’t use excessive force on seized angle stops; forcing them can break plumbing and cause a larger leak.
• Don’t blindly pour chemical drain cleaners into the sink to try to improve faucet pressure—they won’t clear cartridge debris and can damage finishes and seals.

When to Call a Professional

Call a plumber if:

• You can’t identify or access the cartridge or valve body safely.
• The angle stops are seized or leak when you try to operate them.
• Replacing the flex line or cartridge doesn’t restore pressure, or you find corrosion or damage you’re not comfortable repairing.

Safety Notes

• Always turn off the angle stops before disconnecting supply lines. If an angle stop won’t shut, shut off the main water before proceeding.
• Protect finishes by using cloth around pliers and keep small parts in a container to avoid losing them down the drain.
• When flushing the valve body, expect a sudden burst of water—use a bucket and be prepared to catch debris.

Common Homeowner Questions

• Can a clogged aerator cause low pressure? — Yes. Remove and clean it first; it’s a common and easy fix.
• How do I know if the flex line is bad? — Disconnect it and look through; if it kinks or is flattened internally, replace it.
• Will flushing the valve body void anything? — No; flushing is a normal maintenance step, but stop and call a pro if you’re unsure how to reassemble the faucet.