Why is my water heater making popping noises?

A water heater that pops, crackles or rumbles while heating is telling you something about the bottom of the tank. In most cases it isn't dangerous on its own, but it is a sign of wasted energy and extra wear. Here is what each sound usually means.

Popping or rumbling: sediment

Minerals in your water, mainly calcium and magnesium, settle to the bottom of the tank. Small pockets of water get trapped under that layer. When the burner (gas) or lower element (electric) heats them, they turn to steam and escape through the sediment as bubbles. That is the popping you hear. As the layer gets thicker, the popping turns into a deeper rumble.

It is more common in areas with hard water and in gas heaters, because heat comes from the bottom. Sediment also makes the heater less efficient, since the burner has to heat through a layer of mineral before it reaches the water.

What to do: flush the tank. Our step-by-step flushing guide walks through it. If the tank hasn't been flushed in years, one flush may not remove hardened scale; some plumbers use a descaling solution approved by the manufacturer. In very hard water areas, a water softener reduces how fast sediment builds up.

Other sounds and what they mean

Sound	Likely cause	Level of concern
Popping, crackling, rumbling	Sediment at the bottom of the tank	Low to moderate. Flush it.
Sizzling or hissing (gas)	Condensation dripping onto the burner, common when the tank fills with cold water	Usually normal if it fades as the tank heats. Check for leaks if it persists.
Sizzling (electric)	Sediment covering the lower element	Moderate. Flush the tank.
Ticking or tapping	Pipes expanding and contracting, or heat trap fittings	Low. Usually harmless.
Screeching or whistling	A partly closed valve restricting flow	Moderate. Make sure the supply valve is fully open.
Hissing from the side valve	The temperature and pressure relief valve releasing water or steam	High. See below.

When noise comes with warning signs

The temperature and pressure (T&P) relief valve is the safety device on the side or top of the tank, with a pipe running toward the floor. If it is hissing, dripping or discharging water, the tank may be overheating or over-pressurized, or the valve may be failing. Don't plug or cap it. Turn the heater off (breaker for electric, gas knob to off or pilot for gas) and call a plumber.

Also take these signs seriously:

• Water pooling around the base of the tank
• Rusty or discolored hot water
• A smell of gas near a gas heater (leave the house and call your gas utility from outside)
• Loud banging that started suddenly

Is it time to replace the tank?

Popping in a tank that is 10 or more years old, combined with rusty water or moisture at the base, usually means the tank is near the end of its life. Sediment itself doesn't cause leaks, but the conditions that create heavy sediment often go hand in hand with corrosion. See our guide to how long home systems last for typical ranges.

How to keep it quiet

• Flush once a year, or every six months with hard water.
• Keep the thermostat around 120°F. Higher temperatures speed up mineral buildup and raise scald risk.
• Have the anode rod checked every few years.
• Consider a water softener if your water is very hard.