Water Heater Making Noise: What Each Sound Means

By Ray Bennett · Updated 2 October 2026 · 7 min read · Checked against the sources at the end

Water Heater Making Noise: What Each Sound Means

Short answer

A water heater making noise is nearly always sediment. Rumbling, popping and banging while it heats is water boiling underneath a crust of scale on the bottom of the tank, and a flush is the fix. Ticking is only pipes. A hiss at the small valve on the side is pressure, and that is the one sound worth acting on today.

A water heater making noise is usually telling you about sediment, not about a part that is about to fail. The rumble, the popping and the deep banging while it heats all come from the same crust on the bottom of the tank.

The one sound that is different is a hiss from the small valve on the side, and that one is worth dealing with today.

Before you start

What to carry: a garden hose, a bucket and a flathead screwdriver. About an hour for the flush, and most of that is standing and waiting for the tank to empty.

Gas or electric? It changes what the noise means. A gas heater burns under the bottom of the tank, so a crust of scale sits between the flame and the water and steam has to fight its way out through it. An electric heater has two elements reaching into the tank instead, and the lower one ends up buried in that same crust, which is why it burns out years early.

When does the noise happen? Only while it is heating, which points at sediment. Only when a tap is running, which points at a valve. All the time, which is usually a pipe or a pump elsewhere in the house.

One noise means stop rather than diagnose. A hard hiss or a steady drip from the temperature and pressure valve on the side of the tank, with hot water coming out of the discharge pipe, means the tank is letting pressure off. Together with a kettle like boiling sound, treat it as the tank running too hot. Shut the gas off, or the breaker, and shut the cold water valve into the top of the tank. That valve is the last defence a water heater has, so a valve that keeps opening is a fault to fix rather than a noise to live with.

What the noise is telling you

Five noises, five different places. Only the bottom two are the sediment ones, and only the valve is urgent.

What you hear	What it is
Rumbling, popping, deep banging while it heats	Sediment on the bottom. Water boiling under the crust and breaking through
Crackling or sizzling on an electric heater	The lower element buried in that sediment
Sizzling on a gas heater just after a long shower	Condensation dripping onto the burner. Normal, and it stops as the tank warms
Screeching or a high whistle while water runs	A valve that is not fully open, squeezing water through a narrow gap
Ticking or tapping	Pipes expanding, or the heat traps in the fittings on top. Nothing is wrong
A single bang when a tap or a washing machine shuts off	Water hammer in the pipes. Not the heater at all
Humming on an electric heater	An element vibrating in the flow. Tightening it usually settles it
Hissing at the small valve, with water in the discharge pipe	Pressure being let off. The one to deal with now

Why sediment makes that much noise

Hard water carries calcium and magnesium in it. Heat the water and they drop out of it as a white grit, which settles on the bottom of the tank and hardens into a layer over the years.

On a gas heater the flame is under that layer. Water gets trapped in the crust, boils, and the steam bursts out through it, which is the popping and the rumbling. It sounds violent and it is not dangerous, but the tank is now heating through a blanket, so it burns more gas for the same shower.

On an electric heater the lower element sits in the grit, overheats because it cannot shed its heat into the water, and fails. If your noise is crackling and the hot water also runs out faster than it used to, that is the lower element going: how to test a water heater element is a ten minute job with a meter.

Flushing it, which is the actual fix

The last step is the one that matters. An electric element switched on in an empty tank is destroyed in seconds.

Check 1Free, an hour

Drain it and stir it, do not just empty it

Power or gas off first. On a gas heater Rheem says to shut the gas off at the gas control, so turn the dial to OFF. On an electric one switch the breaker off.

Close the cold water valve going into the top of the tank, put a hose on the drain valve at the bottom and run it outside or into a bucket. Open a hot tap somewhere upstairs, or the tank will not drain because nothing can get in behind the water.

Once it is empty, open the cold inlet in short bursts. That is what lifts the grit off the bottom and carries it out of the hose. Emptying a tank quietly and refilling it does very little. The bursts are the whole job.

Keep going until what comes out of the hose runs clear.

Check 2

Nothing comes out of the hose

Check the hot tap upstairs is actually open first, because a sealed tank holds its water.

If it is open and still nothing moves, the plastic drain valve is blocked with the same grit you are trying to remove. Poke it through with a flathead screwdriver or a straightened coat hanger, with the bucket ready, because it usually lets go all at once.

A tank that does this is worth a brass full port ball valve in place of the plastic one. It flushes properly every year after that instead of clogging.

Check 3

It still rumbles after a good flush

A tank that has never been flushed can have a layer that has gone hard, and water alone will not lift it.

Drain it, close the drain, put a few gallons of white vinegar or a proper descaling solution in through the anode rod opening or the hot water outlet, leave it overnight, then drain and flush again.

If the rumble is still there after that, the crust has bonded to the tank. It is noise rather than danger, and on a heater over about ten years old it is not worth chasing any further.

Refill it properly before the power goes back on

Close the drain valve, open the cold inlet, and leave that upstairs hot tap running until the water comes out steadily with no spitting. That is the tank full and the air out of it.

Only then switch the breaker on, or relight the pilot and turn the gas dial back to its normal setting. An electric element switched on in a tank that is not full burns out in seconds, and people who have flushed a heater and then had no hot water at all have usually done exactly that.

A.O. Smith says a gas tank takes about 30 to 40 minutes to heat up fully and an electric one 60 to 90, so give it that long before judging the result.

The noises that are not sediment

Screeching or whistling. Water forced through a gap that is too small. Check that the valve on the cold inlet is fully open, and the shutoff under any tap that screeches. An old gate valve that has been part closed for years is the usual one.

Ticking. Copper expands when hot water runs through it and rubs against the hole in a joist. Harmless, and the only cure is finding the spot and packing it.

A single hard bang when something shuts off. Water hammer. The moving water has to stop suddenly and the shock goes down the pipe. An arrestor fitted at the washing machine or the dishwasher absorbs that shock.

A hum on an electric heater. The element vibrating. Switch the breaker off, take the panel off and check the element is properly tight.

A tankless unit that whines or rattles. The fan and the flow sensor make noise normally. A rattle usually means scale in the heat exchanger, and those need descaling on a schedule rather than when they complain.

Questions people ask

Is the popping dangerous?

No. It is steam getting out from under the scale. It costs you money in wasted fuel and it shortens the tank’s life, but it is not going to burst.

How often should I flush it?

Whirlpool says to drain and flush the tank every six months, and Rheem suggests draining a few quarts every month. A heater flushed regularly from new rarely rumbles at all.

It got louder right after I flushed it.

You loosened the crust without carrying all of it out. Flush it again with more of the short bursts on the cold inlet.

There is water on the floor as well as a noise.

Deal with the water first, and find out where it is actually coming from: finding where a water heater is leaking.

It rumbles and the water is not as hot as it was.

That is the pair that points at the lower element or a thermostat rather than noise alone. Work through it in order instead of guessing at a part.

How old is too old to bother flushing?

Past about twelve years a flush can dislodge scale that was quietly sealing a weak spot, and the tank starts weeping afterwards. Flush a young heater religiously and leave an old one alone.

Sources: Rheem use and care manual AP23698 (rumbling, sizzling, relief valve popping, water hammer, draining), Whirlpool Energy Smart use and care guide 318686-001 (water heater sounds, draining and flushing, filling before power) and A.O. Smith "How Long Does It Take a Water Heater to Heat Up?" (heat up times)