Water heater making noise: what the sounds mean

By Daniel Brooks, Home maintenance writer and appliance troubleshooting specialist based in Charlotte, NC. Reviewed [date — human adds].

Quick answer

Popping or rumbling from a water heater almost always means sediment buildup at the bottom of the tank, while a high-pitched whine or knocking in the pipes usually points to water pressure or a loose fitting rather than the tank itself. The type of sound narrows down the cause quickly, before you need to touch anything. This page covers noise specifically; if there's also active water on the floor, the full water heater diagnostic guide is the better starting point.

Safety first

There's no active leak here, so the risk level is lower than the leaking pages in this cluster. But if the noise is paired with any smell of gas, treat it like a gas-safety issue, not a noise issue, and leave the area immediately rather than trying to identify the sound first.

Popping or rumbling: sediment buildup

This is the most common noise complaint on a water heater. Minerals from the water supply settle at the bottom of the tank over years, and as the burner or heating element heats water through that layer, trapped pockets of water pop and rumble as they escape through the sediment.

Flushing the tank clears it. At a high level: shut off the power (electric) or the gas control (gas units) and the cold-water supply, attach a garden hose to the drain valve near the bottom of the tank, and drain and refill once or twice. Doing this roughly once a year is a common baseline recommended across manufacturer guidance, such as owner's manuals from brands like Rheem, A.O. Smith, and Bradford White, with more frequent flushing worth considering in hard-water areas. A full flush is worth doing on that kind of schedule to prevent buildup, not only after the popping has already started.

Knocking or banging in the pipes: water hammer

This is a different cause entirely, and it isn't the tank itself. A sudden knock right when a faucet shuts off, or when an appliance's water valve closes, is usually water hammer, a pressure wave moving through the pipes rather than anything wrong with the water heater. If it's persistent, a plumber can address it with an air chamber or a hammer arrestor installed near the affected fixture.

Whining or high-pitched sounds

This is usually tied to water flow through a partially closed valve or unusually high water pressure, rather than the tank itself. Check that the cold-water inlet valve feeding the unit is fully open, since a valve that's only partway open can produce a whine as water moves through the restriction.

When a noise means something more serious

A loud bang or a hissing sound paired with any sign of leaking.
A noise that's new and paired with reduced hot water output, which may point to a heating element or burner problem rather than sediment.
Any noise alongside a smell of gas.

Photos for this guide

Flushing sediment from a water heater through the drain valve. — Real photo of a water heater's drain valve with a hose attached for a flush.

FAQ

Why does my water heater make a popping sound?

Popping or rumbling almost always means sediment has built up at the bottom of the tank, and small pockets of water trapped under that layer boil and pop as the unit heats. Flushing the tank clears the sediment and typically stops the noise.

How do I flush sediment out of a water heater?

Shut off the power (electric) or gas control (gas units) and the cold-water supply, then connect a garden hose to the drain valve near the bottom of the tank and let it drain into a floor drain or outside. Refilling and repeating once or twice clears most sediment; check your model's manual for any brand-specific steps or interval.

Is a knocking sound in my pipes related to my water heater?

Not usually. A knock or bang that happens right when a faucet or appliance valve shuts off is typically water hammer, a pressure wave in the plumbing itself, rather than a problem inside the water heater. A plumber can address it with an air chamber or hammer arrestor if it's frequent.

Should I be worried if my water heater suddenly gets louder?

A gradual increase in popping as sediment builds up over months or years is normal and worth addressing with a flush. A sudden, loud noise that's new, especially paired with reduced hot water or any sign of a leak, is worth checking more closely rather than assuming it's routine sediment.