Quick Answer:
If only one tap pulses, first check the aerator and cartridge. Remove the aerator and watch the flow; then flush the hot and cold supplies into a bucket and clean the cartridge. If pulses continue after cleaning, you’re likely dealing with loose debris upstream of the cartridge or an intermittently failing ceramic disk cartridge.
Why This Happens
- The issue is usually localized to that fixture, not the whole house supply.
- Small bits of grit or mineral scale can move and partially block flow at the aerator, valve, or inside the cartridge, causing a pulsing or surging effect.
- Some cartridge types—especially ceramic disk cartridges—can begin to fail intermittently as the seals chip or wear, producing on/off flow even when the handle is steady.
- If you hear other noises or see different symptoms, see the note about related issues like One faucet whistles under low pressure.
Step-by-Step What to Do
1. Remove the aerator and observe
- Unscrew the aerator screen from the spout (use pliers with a cloth if it’s tight).
- Turn the tap on and watch the flow. If the pulsing stops, the aerator was trapping shifting debris—clean or replace it.
2. Flush both supplies into a bucket
- Shut off any nearby shut-off valves if you have them; otherwise work carefully to avoid splashing.
- Remove the cartridge access (this may require removing the handle and trim). Place a bucket under the spout outlet or valve body.
- Turn the hot and cold supplies on briefly, one at a time, to flush debris out into the bucket. Don’t run for more than a few seconds at full force to limit mess.
3. Clean the cartridge
- Take the cartridge or valve insert out and inspect for grit, scale, or damage.
- Rinse it under clean water and gently remove deposits with a soft brush. For mineral scale, use a vinegar soak for a short time, then rinse thoroughly.
- If you see chips, deep scratches, or a cracked seat, plan to replace the cartridge. Intermittent pulsing is a common sign of a failing ceramic disk cartridge.
4. Reassemble and test
- Put the cartridge and trim back in place, restore supplies, and test the tap with the aerator off first, then with it on.
- If the pulsing is gone, you’re done. If it returns, proceed to the next step.
5. If pulses continue
- Assume that loose debris is still present upstream of the cartridge or that the cartridge is failing intermittently.
- Either replace the cartridge with a proper OEM or compatible part, or call a plumber to locate and remove any debris trapped in the valve body or supply lines.
What Not to Do
- Don’t keep living with pulsing—loose debris can suddenly lodge and stop the fixture completely.
- Don’t force parts or use excessive heat to loosen fittings; you can crack trim or damage seals.
- Don’t ignore visible damage to the cartridge; a compromised cartridge will usually need replacement rather than a temporary patch.
When to Call a Professional
- If you can’t access the cartridge or valve without cutting into the wall or removing tile.
- If flushing doesn’t clear the pulses and replacing the cartridge doesn’t fix it—there may be debris lodged deeper in the valve or the supply line that needs tools and experience to remove safely.
- If you find corrosion, cracked valve bodies, or any signs of active leaks when you disassemble the fixture.
Safety Notes
- Shut off water to the fixture at the shut-off valves before taking the cartridge out when possible.
- Work with a bucket and towels to catch water when you open the valve. Wear gloves and eye protection if you expect spray or dirty water.
- If you use a vinegar soak for scale, rinse parts thoroughly before reinstalling to avoid lingering acidity on seals.
Common Homeowner Questions
- Why does only one tap pulse? The problem is most likely inside that fixture—debris, the aerator, or the cartridge—rather than a whole-house pressure issue.
- Can I keep using it until I buy parts? No. Continued use may force debris into a position that fully blocks flow; clean and test now or turn the fixture off until fixed.
- Is a cartridge replacement DIY? Many are, but if the valve is seized, buried, or part of a complex trim set, call a pro. For different fixtures see related topics such as Tub spout low pressure but showerhead fine.
For more related articles, see the Low Pressure at Single Fixture hub.