Quick Answer:
If only the cold tap sputters air while the hot tap is normal, the issue is usually trapped air or a restriction on the cold side of that fixture. Start by comparing cold and hot at the same faucet, then purge the cold feed slowly and check the cold stop valve and any filter or check device feeding that fixture.
Why This Happens
Air can enter the pipes for a few common reasons: recent winterization, turning a supply back on, work on the water line, or a partially closed valve that lets air collect before water pushes through. If the problem is limited to cold water, the air or restriction is on the cold feed side — often at the shutoff under the sink, an inline filter, or a check valve. If you recently winterized or turned your system back on, trapped air is a likely cause; see Air pockets after winterization and Air bubbles after turning water back on for related situations.
Step-by-Step What to Do
1. Compare cold vs hot at the same fixture
Turn both taps (or the single-handle faucet to full hot and full cold) and observe flow. If hot is steady and cold sputters, the problem is on the cold side of that fixture or its supply line.
2. Check other fixtures
Test other sinks, showers and outside taps. If only one fixture sputters, the issue is local. If many fixtures show the problem, it’s likely a house-wide cold supply issue.
3. Run the cold slowly to purge air
Open the cold tap slowly and let it run for several minutes. Running it gently flushes trapped air without causing pressure surges. If air clears and flow becomes steady, the problem was air in the line.
4. Inspect the cold stop valve at the fixture
Locate the shutoff valve under the sink or behind the fixture and confirm it is fully open. A partially closed or gritty valve can trap and release air or reduce flow. If the valve is hard to turn or leaks, consider replacing it, but only after confirming the valve is the issue.
5. Check any filter, aerator or check devices on the cold feed
Many fixtures have small inline filters, backflow preventers, or faucet cartridges that affect only the cold inlet. After running the cold until flow stabilizes, remove the aerator and inspect for debris. If the sputter is isolated to one faucet, cleaning the aerator often helps. If there is an inline filter or stop with a screen, follow the manufacturer’s instructions to inspect or clean it.
6. Watch for patterns after purging
If the cold clears but returns later, note when it happens (after using appliances, following water meter activity, or after the water main is worked on). Persistent or recurring air indicates a deeper issue that may need professional attention.
What Not to Do
- Don’t swap cartridges right away; confirm it’s not a cold-side feed issue or a partially closed stop valve.
- Don’t open the main supply fully and suddenly — that can force debris and air into fixtures.
- Don’t force or wrench valves that are stuck; you can break the valve or packing and cause a leak.
When to Call a Professional
- If air sputtering affects the entire house or multiple fixtures after purging.
- If you find a failing shutoff, cracked pipe, or leak while inspecting valves or fittings.
- If air returns repeatedly or is paired with low water pressure or visible sediment — this can indicate a failed pressure regulator, water main work, or a problem with the municipal supply.
Safety Notes
- Shut off the water at the main if you discover a leak you cannot control.
- Avoid standing water near electrical outlets or appliances when testing taps.
- If you disconnect any plumbing device (filters, cartridges, etc.), follow manufacturer instructions and be ready to catch water; use towels and a bucket.
Common Homeowner Questions
- Why does only cold sputter? Because air or a restriction is on the cold supply side — often a partially closed stop valve, inline filter, or trapped air in the cold line.
- Will running cold longer fix it? Often yes for trapped air; run the cold slowly for several minutes to purge the line. If it returns, further inspection is needed.
- Could this damage fixtures? Generally no, but repeated pressure spikes or debris can harm cartridges or aerators over time; inspect these parts if the sputter persists.
Related Articles
If you’re troubleshooting a similar symptom, these guides may help:
For the full directory, see Air in Pipes After Shutoff.