Quick Answer:
If pressure at one sink feels weaker or stronger after a repair, it’s usually a simple supply or aerator issue rather than deliberate valve changes. Start by comparing water flow at nearby fixtures for reference, then check the sink aerator and the shutoff valves under the sink. If nothing obvious shows, stop and call a plumber.
Why This Happens
Common causes for a visible pressure change after work on a sink include:
- Partially closed supply valves under the sink after the repair.
- Dislodged debris or mineral build-up caught in the aerator or faucet cartridge.
- Shifts in a mixing cartridge or diverter that change how hot and cold blend.
- Air trapped in the line right after valves were opened, briefly reducing flow.
- Less common: a pressure regulator or main shutoff being moved, or damage to a supply line.
If the repair also touched the drain, you might notice related symptoms like a slow sink or strange drainage. See notes on related topics such as Sink backs up after remodel and Drain performance changed after repair for drain-focused issues.
Step-by-Step What to Do
Step 1: Compare pressure at nearby fixtures for reference
Turn on a nearby sink, a bathroom tap, or an outside hose to see if pressure change is only at the repaired sink or affects other areas. If only the repaired sink is affected, the issue is local to that fixture. If multiple fixtures are low, it’s likely a house supply or pressure regulator issue.
Step 2: Check the faucet aerator
- Unscrew the aerator at the end of the spout (use pliers with a cloth if tight).
- Rinse out debris and mineral deposits, then reassemble and test flow.
Step 3: Inspect under-sink shutoff valves
- Locate the hot and cold shutoff valves under the sink. Confirm they are fully open (turn counterclockwise until they stop).
- If the valves are quarter-turn ball valves, make sure the handle lines up with the pipe direction.
Step 4: Flush the lines
- With aerator removed, briefly open both shutoffs and run water to flush any debris. Have a bucket or towel ready.
- Close shutoffs, replace aerator, and test the faucet.
Step 5: Check the faucet cartridge or cartridge-style faucet
- If the faucet still has poor flow, the cartridge or ceramic disc may be clogged or misaligned. Turn off water, disassemble per the manufacturer’s instructions, and inspect for debris.
- Replace the cartridge if damaged or corroded.
Step 6: Look for whole-house signs
- Check other fixtures again and the water heater performance. A failing pressure regulator or a main shutoff partly closed can affect multiple points.
What Not to Do
- Do not adjust valves blindly to fix pressure. Turning things randomly can cause leaks or let too much water into a work area.
- Do not use excessive force on plastic fittings or cartridges — you may crack them.
- Do not pour strong chemical cleaners into a drain to fix a pressure issue; the problem is usually supply-side, and chemicals can damage pipes and fixtures.
When to Call a Professional
- There’s no improvement after checking aerator and shutoff valves, or multiple fixtures show problems.
- You find leaking or damaged supply lines, or a shutoff valve that won’t open/close properly.
- The pressure regulator (often near the main shutoff) seems to be failing or the main supply is affected.
- You’re uncomfortable disassembling the faucet or replacing a cartridge.
Safety Notes
- Turn off the shutoff valves before removing cartridges or disconnecting supply lines.
- Release trapped hot water from lines carefully to avoid scalding.
- Use basic protective gloves and eye protection when working under the sink.
- If you smell gas or see signs of major damage, evacuate and call a professional immediately.
Common Homeowner Questions
- Why did the pressure drop right after the repair?
Often a valve was left partly closed or debris was dislodged into the aerator or cartridge. - How long should I try fixes before calling a plumber?
After 15–30 minutes of the simple checks listed above, call a pro if the problem persists or if you see leaks. - Can I fix a pressure regulator myself?
No — pressure regulators are part of the main supply and are best handled by a licensed plumber because they affect the whole house.