Call a plumber: likely sediment in the tank

Why this happens

A. O. Smith says popping can come from sediment that traps steam bubbles at the bottom of the tank, and that the bubbles make a pop when they break free. It adds that the layer also stops the water from warming efficiently. Rheem says sediment buildup is the most common cause of popping or rumbling in tank-style heaters, and A. O. Smith says that while it is not dangerous, sediment reduces efficiency and accelerates tank wear. Bob Vila says long-term uneven heating and pressure can damage the tank's lining, and that left alone the tank could eventually crack or leak. Bob Vila also says an occasional crackle on a gas heater can be condensation vaporizing on the burner, and a plumber can confirm which it is. A. O. Smith and Rheem both name flushing as the cure, but sources differ on whether a homeowner should drain a tank. A. O. Smith and Rheem describe owners doing it, while Bradford White says to ask your plumbing professional about draining, and This Old House says forcing a clogged drain valve can cause leaks. On this site, flushing is left to the plumber.

What to do right now

1. If you smell gas, or hear hissing near a gas line or the burner, leave the house and call 911 and your gas utility from outside.
2. Notice when it happens: only while the heater is heating, after a lot of hot water was used, or also when no water is running. A. O. Smith says a pro may ask about this, plus how long it has gone on and when the heater was last serviced.
3. Look from a distance with a flashlight at the base of the tank and the relief valve pipe, the pipe that runs down from the relief valve near the top or side of the tank. If you see water or steam, keep away from the end of the relief valve pipe, never block it, and call a licensed plumber right away, because that is more urgent than the noise.
4. Do not open the heater's panels. Do not drain or flush the tank yourself, and do not touch the relief valve. On this site flushing is left to the plumber, and Rheem's relief valve bulletin warns that water drained from a heater will be hot.
5. Call a licensed plumber or an authorized water heater service provider to inspect the heater and deal with the sediment. Tell them how long the noise has gone on and when the heater was last serviced.

When to stop. Water or steam from the relief valve pipe means keep away from the end of the pipe, never block it, and call a licensed plumber right away. Water coming from under the tank, or hissing or sizzling, means stop using the heater and call a licensed plumber. Smoke, flames, sparks or a burning smell near the heater mean leave the house and call 911 from outside. A gas smell, or hissing near a gas line or the burner, means leave and call 911 and your gas utility from outside.

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