Why Is My Water Heater Making Noise?

Popping and rumbling

A popping, crackling or low rumbling sound while a tank heater is heating is the most common water heater noise, and it almost always points to sediment. Hard water leaves calcium and magnesium on the bottom of the tank. Water trapped under and inside that layer gets superheated, forms steam bubbles, and the bubbles collapse with a pop. On a gas heater you hear it most just after the burner lights. On an electric heater it can come from the lower element when sediment buries it.

The noise itself is not dangerous, but it tells you the heater is working harder than it should. The burner or element runs longer, the bottom of the tank runs hotter, and the tank ages faster. If the sound has gone from occasional to constant, the sediment layer is probably thick.

• A newer tank that pops lightly: flushing it per the manufacturer's instructions often quiets it.
• An older tank that rumbles loudly: heavy sediment may not flush out, and the tank may be near the end of its life.
• A tankless unit does not collect sediment the same way, but scale on its heat exchanger can cause similar crackling. It needs descaling, as described in the owner's manual.

Ticking and tapping

A ticking or tapping sound, often from the pipes above the heater, usually comes from metal expanding and contracting as hot water starts and stops moving. Many tanks also have heat trap fittings in the inlet and outlet connections that can tick as water flows. This is usually harmless. If it is loud enough to bother you, a plumber can look at how the pipes are strapped and whether the fittings are the source.

Hissing and sizzling

Hissing and sizzling need more attention, because the cause can range from harmless to a leak.

• Sizzling on a gas heater right after the burner lights can be condensation dripping onto the burner, which is fairly common on a cold tank filled with cold water. If it stops once the tank warms up, it is probably condensation.
• Sizzling that continues, or water you can see on the floor or the burner area, can mean the tank is leaking. Shut off the cold water supply to the heater and call.
• Hissing on an electric heater can come from scale on the heating elements.
• Hissing or dripping at the temperature and pressure relief valve, the valve on the side or top of the tank with a pipe running down toward the floor, means the valve is releasing water. That can mean the tank is getting too hot or the pressure is too high. Treat it as a service call, and never cap, plug or remove that valve or its pipe. It is the part that keeps an overheated tank from failing violently.

Screeching, humming and banging pipes

A high-pitched screech or whistle while water is running often means water is being forced through a partly closed valve, such as the cold inlet valve at the top of the tank. Make sure that valve is fully open. If the sound continues, the valve or a fitting may be failing.

A steady hum on an electric heater is usually a heating element vibrating as water moves around it. It is generally harmless, though a loose element is worth having checked.

A loud bang in the pipes when a faucet, washing machine or dishwasher shuts off is called water hammer. The heater may be where you hear it, but the cause is the sudden stop of moving water in the lines. High house water pressure makes it worse. A failing pressure regulator, or no regulator at all, is a common reason, and it is worth fixing because repeated hammer and high pressure strain pipes, fittings and the heater.

What you can safely check yourself

Do not open the burner compartment, adjust the gas control, remove element covers on an electric heater with the power on, or try to test the relief valve on an old tank, which can stick open and leak. Those are jobs for a trained technician.

1. Note what the sound is, when it happens and how long it lasts. A short phone video helps.
2. Look around the base of the tank and under a tankless unit for water.
3. Confirm the cold water valve at the top of the tank is fully open.
4. Look at the relief valve discharge pipe. If the end is wet or dripping, mention it when you call.
5. Check the temperature setting against the range on the heater's label.
6. Read the label for the model and serial number, so the plumber knows what the heater is and roughly how old it is.

Noises that need a plumber now

Some sounds are a reason to stop and call instead of waiting to see if they go away.

• Any noise combined with the smell of natural gas. Leave the house, then call the gas utility or 911 from outside.
• Hissing or steady discharge from the relief valve.
• Sizzling with water on the floor or on the burner.
• Loud banging or rumbling from a tank that also shows rust or leaks.
• Water too hot to touch at the tap, which is a scald risk, especially for children and older adults.

When a noisy heater is worth fixing

On a heater that is a few years old, the fix for most noises is simple: flushing sediment, opening a valve, replacing an element, or correcting high water pressure. On a tank near or past ten years with heavy sediment, the noise is often a sign the tank is close to the end, and spending money on it may not make sense. A plumber can look at the age, the sediment and the condition of the tank and tell you which way it leans.

Rocket repairs and replaces tank, tankless and heat pump water heaters across the Salt Lake Valley, and installs water softeners that reduce the sediment behind most of these noises. Call or text (385) 722-7638 and describe the sound.