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Water heater making noise: popping, rumbling, hissing and what they mean

Most water heater noises come from sediment, expanding metal, or water moving through valves, and many are harmless. A few point to a pressure or safety problem. Here's how to match the sound to the cause and decide what to do.

Safety first. If the noise is a loud hiss or scream coming from the temperature and pressure (T&P) relief valve, or water or steam is shooting from its discharge pipe, turn off the heater's energy (breaker or gas control) and call a plumber. If you smell gas, leave the house and call your gas utility or 911 from outside. Never cap or plug the relief valve.

Popping, rumbling or crackling

This is the most common complaint, and it's usually sediment. Minerals in hard water settle into a layer at the bottom of the tank. Water gets trapped under that layer, overheats, and bursts up through it as steam bubbles, which you hear as popping or rumbling. It's often loudest on gas heaters, where the burner heats the tank bottom directly, and during a long heating cycle after heavy hot water use.

What to do: flush the tank following the manufacturer's instructions. Turn off the energy, shut the cold supply, attach a hose to the drain valve, run it to a drain or outside, and drain until the water runs clear. Briefly opening the cold supply while the drain is open can help stir sediment loose.
Why it matters: heavy sediment makes the heater less efficient and can overheat the tank bottom. On electric heaters, sediment can bury and burn out the lower element.
If flushing doesn't quiet it, the sediment may be hardened. An older, very noisy tank is often a sign it's near the end of its life.

Sizzling or hissing

Gas heater, sizzling near the burner: often condensation dripping onto the flame, which is common when the tank is refilling with cold water and usually stops as it warms up. If it doesn't stop, or you see water pooling in the burner area, check for a leak (see the leak guide linked below).
Electric heater, sizzling or hissing: can be sediment building up on a heating element. Flushing helps; a badly scaled element may need replacing.
Hissing at a fitting or valve: look for a small leak at the top connections, the drain valve, or the relief valve.

Ticking or tapping

Ticking usually comes from pipes and fittings expanding and contracting as hot water flows through them, or from heat traps (small check valves in the inlet and outlet nipples on many heaters). It's generally harmless. If it bothers you, a plumber can swap the heat-trap nipples for standard ones.

Knocking or banging (water hammer)

A bang when a faucet, washing machine or dishwasher valve shuts off quickly is usually water hammer in the house plumbing, not the heater itself. A plumber can add water hammer arrestors, secure loose pipes, or check whether house water pressure is too high.

Screeching, whistling or humming

Screeching or whistling often means water is squeezing through a partly closed valve. Make sure the cold supply valve above the heater is fully open.
A steady hum on an electric heater can be a loose element vibrating as cold water flows past it. With the power off and the tank drained below that level, the element can be checked and tightened.
Whistling or roaring from a gas heater's vent or burner can be a draft or combustion issue. That one is worth having a professional look at.

When to call a plumber

The relief valve is hissing, screaming, or discharging water.
The noise is new and loud and comes with leaking, rusty water, or a burning smell.
A gas heater has an unusual flame, roaring, or soot around the burner.
Flushing doesn't help and the heater is older. Check the label for the serial number, which can tell you its age.

Tip: Record a short video of the noise on your phone, and note when it happens (while heating, right after a shower, when a faucet shuts off). That helps a plumber narrow down the cause quickly.