Water Heater Making Noise: Popping, Rumbling, Hissing

What each noise usually means

Start with the sound. This table covers what manufacturers say about each one.

Rheem's rule of thumb is that sounds are fine when they're "quiet, brief and at regular intervals". A noise that gets louder month over month is telling you something.

Popping and rumbling: sediment

Rheem calls sediment buildup the most common cause of popping or rumbling in a tank. Hard water drops calcium and magnesium as it heats, and the flakes settle on the bottom. On a gas heater that's right where the burner flame hits. On an electric heater the lower element can end up buried in it.

Sediment costs you more than noise. It insulates the water from the heat, so the heater runs longer to do the same job. That's why an old, loud tank often goes with slower recovery and higher bills.

How to flush it

A.O. Smith says most tank heaters should be flushed at least once a year, and more often with hard water. The short version:

1. Turn off the gas or the breaker, and let the tank cool.
2. Close the cold water supply to the heater.
3. Hook a garden hose to the drain valve and run it to a floor drain or outside.
4. Open a hot tap somewhere in the house so air can get in.
5. Open the drain valve and let it run until the water comes out clear.
6. Close the drain valve, refill the tank with a hot tap open until water flows steadily, then restore gas or power.

Never turn the power back on to an electric heater with an empty tank. The elements can burn out without water around them. Our water heater flush guide has the full steps.

One practical thing: the drain valve on most tanks is plastic, and a tank that's never been flushed can clog it with sediment. If the flow slows to a trickle or stops, don't force the valve. A.O. Smith says to call a plumber when sediment blocks the drain.

When flushing doesn't stop the popping

If the tank still rumbles after a good flush, the sediment may be packed too hard to rinse out, or there's simply too much of it. Rheem suggests a professional cleaning for heavy buildup and a pro visit when noise keeps going after flushing. On a tank that's around ten years old, that's also the point to price a replacement.

Crackling

Crackling is often the same sediment problem, just a lighter version. A.O. Smith points to a second cause: an aluminum anode rod reacting with chlorine in the water and shedding beads of aluminum hydroxide. If you see small white or gray beads in the flush water, ask about switching to an aluminum-zinc anode. See anode rod basics for how to check one.

Hissing and sizzling: turn it off

This is the one sound you shouldn't wait on. Rheem lists water dripping onto a hot burner on a gas heater and a leaking element gasket on an electric heater as causes, and says it's safest to turn off the unit and contact a professional.

Look before you call. Water on the floor or running down the tank means you're dealing with a leak, so go to water heater leaking or leaking from the top. A hiss from the pipe on the side of the tank is the T&P valve (temperature and pressure relief valve) letting water out. That has its own causes, covered on relief valve leaking.

Screeching, whistling and banging

A high-pitched whistle usually means water is squeezing through a restriction. Rheem says to check that the inlet and outlet valves are fully open and to look at the household water pressure. On power-vent gas heaters with a blower, A.O. Smith adds a dirty blower wheel, a blocked vent or worn blower bearings to the list, and bearings mean a new blower motor.

Banging when a faucet or the washing machine shuts off is water hammer. It's a plumbing issue more than a heater issue. A water hammer arrestor near the fast-closing valve, plus strapping loose pipes, usually quiets it.

Tankless water heater noises

A tankless unit has no tank for sediment to collect in, but scale still builds inside the heat exchanger. Rheem says tankless units can whistle or hiss when scale restricts flow. A.O. Smith recommends descaling annually, especially in hard water areas. A fan hum and a click at ignition are normal. Grinding or a loud blower is not.

Noise at night

People notice these sounds at night because the house is quiet, not because the heater does anything different. A tank still reheats when it loses heat through the walls, so you'll hear the burner light or the element hum even when nobody's using water. Ticking as pipes change temperature is normal. Rumbling every time it fires is the sediment problem again.

When to call a plumber, and what it costs

Call a plumber if:

• You hear hissing or sizzling, or see water near the burner or element.
• The noise keeps going after a flush, or banging gets louder.
• The drain valve is clogged and won't let the tank empty.
• The tank is in the 8 to 12 year range and getting loud.

HomeGuide lists a tank flush at $75 to $200. A service call alone runs $50 to $200 in many areas. If the noise turns out to be a failing element, replacement runs $100 to $350. Once a repair passes half the price of a new heater, HomeGuide suggests replacing instead. Compare with water heater cost before you decide.