Why a Water Heater Makes Noise

Most water heater noise comes from sediment: minerals from the water that settle in the bottom of the tank and trap pockets of water that boil and pop as the heater runs. That is common in South Florida, where the water is hard, and on its own it is not an emergency. A few sounds are different. A high whistle or a loud bang can mean pressure is building, and rumbling that comes with a leak or rusty water usually means the tank is near the end. The sound itself tells you a lot about which one you have.

Where the sediment comes from

Broward County’s water is drawn largely from limestone, and it carries dissolved calcium and magnesium. When that water is heated, some of the minerals come out of solution and drop to the bottom of the tank. Over months and years they build a layer of grit and scale.

That layer causes trouble in three ways. It traps small amounts of water underneath it, which flash to steam and burst through with a pop. It insulates the water from the burner or the lower element, so the heater runs longer to reach temperature. And on an electric heater, scale can crust over the lower element itself, so it runs hotter than it should and fails sooner.

A tank that is flushed regularly rarely builds enough sediment to be loud. A tank that has never been flushed almost always will in the end.

What each water heater noise usually means

Different sounds point to different causes. Here are the common ones.

Rumbling or popping. The classic sediment sound. Pockets of water under the sediment layer boil and break through. It is often loudest just after a lot of hot water has been used and the heater is working to recover. Light popping in a younger tank can often be cleared by flushing. Heavy, constant rumbling in an older tank means the sediment has hardened and built up for a long time.

Crackling or sizzling. On an electric heater, this can be water boiling against a scaled-up element. On a gas heater, it is often condensation dripping onto the burner, which is common when the tank is filling with cold water and usually stops once it warms. If sizzling comes with water on the floor, look for a leak.

Ticking or tapping. Usually the pipes, not the tank. Metal pipes expand as hot water runs through them and contract as they cool, and they tick against straps or framing. Some heaters also have heat traps, small valves in the inlet and outlet that can tick as water moves. This is mostly harmless, though a pro can quiet it with better strapping or a different fitting.

Knocking or hammering. A bang when a tap or valve shuts quickly is water hammer: the moving water stops suddenly and jolts the pipes. It is not the heater’s fault, but repeated hammering strains fittings and the tank’s connections. An arrestor or a pressure check can fix it.

Humming. On an electric heater, a hum can come from a loose element vibrating as water flows past it. It is usually minor, but it is worth having the element checked.

Whistling or screeching. Water forced through a narrow gap makes this sound. It can be a partly closed valve on the supply line, which is easy to fix. It can also be the temperature and pressure relief valve starting to open because pressure or temperature in the tank is too high. That second case needs attention.

The noises that need a pro now

Treat these as more than a nuisance:

• A screech or whistle from the relief valve, or water discharging from the relief valve’s pipe. The valve is doing its job of relieving pressure, but something is pushing it there. Turn the heater off at the breaker or set a gas heater to its pilot or vacation setting, and call.
• A loud bang from inside the tank, especially a single sharp one. This can mean heavy sediment shifting or overheating. Turn the heater off and have it checked.
• Rumbling with water on the floor. A rumbling tank that is also leaking from the body is finished. A tank cannot be patched.
• Rumbling with rusty hot water. Sediment plus rust in the hot water usually means the inside of the tank is corroding.
• Any noise with a smell of gas. Leave the house, then call your gas utility or 911 from outside.

Which water heater noise means the tank is finished

A noisy tank is not always a dying one. Sediment can be flushed, elements replaced and valves changed. The sound tells you the tank needs attention. Whether the tank is finished depends on what comes with it.

The signs that the noise belongs to a tank at the end of its life:

1. The rumbling has gone on for a long time and has grown louder.
2. Flushing brings out a lot of hard, rocky sediment, or the drain valve clogs with it.
3. The hot water is rusty or brown while the cold is clear.
4. There is rust at the base or around the fittings.
5. Water is seeping from the body of the tank.

If several of these line up, a pro will likely suggest replacement rather than another flush. If the tank is younger and the only sign is noise, a flush and a check of the anode rod is usually the first step.

Should you flush the tank yourself

Flushing a water heater is a routine job, and many owner’s manuals describe it. But it has risks on a tank that has been noisy for a long time. Hard sediment can clog the drain valve so it will not close again. Older plastic drain valves can break. And on a very old tank, disturbing heavy sediment can sometimes open up a leak that the sediment was sealing.

If your heater is young and only mildly noisy, a careful flush following the manufacturer’s instructions is reasonable. If it is older, loud, or you are not sure how to shut off the power or gas safely, leave it to a pro. A pro can also replace a plastic drain valve with a brass one so future flushes are easier.

Keeping water heater noise from coming back

Once the tank is quiet, a few habits keep it that way:

• Have the tank flushed regularly, before the sediment hardens.
• Have the anode rod checked, since a spent rod lets the tank corrode and adds rust to the sediment.
• Keep the thermostat at a sensible setting. Hotter water drops out more minerals.
• Ask whether a water softener or a scale filter makes sense for your home.
• On a tankless unit, have the heat exchanger descaled, since scale there causes its own noises and error codes.

Getting it checked

If your heater has started to rumble, pop or whistle and you want to know what that water heater noise means, One Call Home Pros can arrange it. We match you with a vetted, licensed, insured local professional who listens to it, flushes or inspects it, and tells you whether it needs a repair, a maintenance visit or a new tank. You pay One Call, and One Call pays the pro; ask what the price covers before work starts. You can read more about water heater repair and replacement.

Most noises are a maintenance problem caught early. If yours sounds like more than that, tell One Call what you are hearing and we take it from there.