Quick Answer:
If only the hot taps spit air for a few seconds before flowing normally, the most likely causes are air trapped in the hot side of your plumbing or inside the water heater after it was drained or refilled. First compare hot and cold at the same fixture. Run a single hot fixture until the sputtering stops. If the problem returns after every heater cycle, a valve or mixing/check-valve arrangement may be trapping air on the hot side.
Why This Happens
- Air can enter the system when the heater or hot branches are drained, replaced, or refilled. That air tends to collect on the hot side first.
- If cold taps are normal while hot taps spit air, the issue is confined to the hot side—either the tank, the hot manifold, or a check/mixing valve that traps pockets of air.
- Some plumbing layouts and valves let air collect in a loop that only moves when the heater refills or cycles, so you get repeated sputtering after the tank refills or heats.
Step-by-Step What to Do
1. Compare hot vs cold at the same faucet
- Open the cold then the hot at the same fixture. If cold is steady and hot spits air, the problem is limited to the hot side.
2. Run one hot fixture until it clears
- Choose a single sink or tub and run the hot water at a moderate flow. Keep it running until the sputtering stops and the flow is steady. This often pushes trapped air out of the hot branches.
3. Note timing and pattern
- If the sputter appears only right after refilling or after the heater comes on, write down when it happens. If it returns after every heater cycle, the pattern suggests air is re-entering a trapped section.
4. Check recent work or meter/service changes
- Think about recent plumbing work, water meter replacement, or water main work that might have introduced air. If you suspect a recent refill, the issue may be similar to situations described in Air trapped after meter replacement.
5. Inspect visible plumbing and valves
- Look at accessible piping and any mixing valves or check valves on the hot outlet. A check valve or anti-return device can hold air in a hot loop and make the sputter repeat after tank cycles.
6. Restart the water heater carefully
- If you turn the heater off to work on plumbing, be aware that refilling the tank may introduce more air. After refilling, run a hot fixture to purge the air. If sputtering resumes after every refill or heating cycle, note that for a technician.
What Not to Do
- Don’t bleed the water heater aggressively if you’re unsure about the setup—heater-side mistakes can cause damage.
- Don’t remove pressure-relief valves or make boiler-style alterations yourself. Those parts are safety devices and must be handled correctly.
- Avoid rapid flushing or disassembly of the heater plumbing without knowing whether check valves or mixing valves are present; you can push air into other branches or cause cross-connections.
When to Call a Professional
- Call a plumber if the sputtering continues after you’ve run a single fixture until clear, or if the sputter returns consistently after each heater cycle.
- Also call a pro if you find a check valve, mixing valve, or a complicated manifold and you are not sure how it should be configured—those can trap air and require valve adjustment or re-plumbing.
- If you smell gas after working near a gas water heater, or if the heater shows error lights and the sputter coincides with heater faults, stop and call a technician immediately.
Safety Notes
- Hot water can scald. When running hot water to purge air, keep the flow moderate and test temperature before putting hands under the stream.
- Turn off electrical power or gas to the heater only if you know how and why you are doing it. If you’re unsure, leave electrical or gas isolation to a qualified technician.
- Do not remove safety devices such as pressure-relief valves. Those protect you from overpressure and should only be serviced by professionals.
Common Homeowner Questions
- Why does only the hot spit air? Because the air is trapped in the hot branch or tank; the cold side is separate so it remains steady.
- Will running the hot for a while fix it? Often yes—running one fixture will purge trapped air, at least temporarily.
- Could recent meter or service work cause this? Yes. If you recently had work done, the situation can be similar to Cold water spits air only or other cases where air was introduced during service.
Related Articles
If you’re troubleshooting a similar symptom, these guides may help:
For the full directory, see Air in Pipes After Shutoff.