Water Heater Making Noise? A Sound-by-Sound Guide

A new noise from the basement or utility closet is hard to ignore. Most water heater sounds have a simple cause, and many are fixable in an afternoon. If you would rather have someone handle it, our water heater maintenance service in Newark includes a flush and a full check of valves and pressure. This guide covers what each sound means, what you can safely try and when to call. It applies to tank-style gas and electric heaters, with a short section on tankless units.

Why is my water heater making noise?

The most common reason is sediment. Tap water carries dissolved minerals such as calcium and magnesium. When water heats, some of those minerals drop out and settle on the tank bottom as a crusty layer.

Water gets trapped under that layer. As the burner or element heats it, the trapped water flashes into steam bubbles. The bubbles burst up through the sediment and make popping or rumbling sounds. Both Rheem and A. O. Smith name sediment as the main cause of these noises.

Other causes include:

• Scale on electric elements, which makes them hiss or sizzle
• Water dripping on a hot gas burner, from condensation or a leak
• Water hammer in the pipes, from fast-closing valves
• A restricted valve or partly closed shutoff, which can whistle
• High water pressure or thermal expansion, which can make knocking sounds

Water heater noises: what each sound means

Use this table to match the sound to the likely cause.

Why is my water heater popping?

Popping is the classic sediment sound. It is louder in gas heaters because the burner heats the tank bottom directly. In hard-water areas it can start within a few years.

Popping matters for three reasons:

• Wasted energy. Heat has to pass through the mineral layer before it reaches the water.
• Overheated steel. The tank bottom runs hotter than it should, which can weaken the glass lining.
• Lost capacity. A thick layer takes up room and can clog the drain valve.

The fix is to drain and flush the tank. Our step-by-step guide on how to flush a water heater walks through it.

Why is my water heater knocking?

Knocking or banging usually starts in the pipes, not the tank. When a washer or dishwasher valve snaps shut, moving water slams to a stop. That shock wave is called water hammer.

Try these steps:

1. Note when it happens. If it follows the washer or dishwasher filling, it is likely water hammer.
2. Check house pressure with a gauge on an outdoor spigot. Over 80 psi makes water hammer worse.
3. Look for loose pipe straps near the heater.
4. Ask about water hammer arrestors, small shock absorbers installed near fast-closing valves.

Knocking that happens while the heater runs can also come from pressure building in a closed system. That points to a missing or failed water heater expansion tank.

Why is my water heater whistling or screeching?

A high-pitched sound means water is squeezing through a narrow opening. Check these, in order:

1. The cold shutoff valve above the heater. If it is only part open, open it fully.
2. The relief valve. A valve that is weeping can whistle. Check the end of its discharge pipe for water.
3. Pipe fittings with mineral buildup inside.

If the sound stays after you open the valves, have the heater looked at. A whistle from the relief valve area means pressure or temperature may be too high. Our guide to a water heater pressure relief valve leaking explains the test.

Hissing and sizzling sounds

On a gas heater, a short sizzle when the burner first lights can be normal. Cold water makes condensation on the outside of the tank, and drops land on the flame.

Sizzling that lasts, or comes with puddles, is different. It can mean the tank or a fitting is leaking onto the burner. On an electric heater, hissing often means scale on an element or a leaking element gasket.

If you see water near the burner or under an element cover, turn off the gas or power. Then call for service.

Should a water heater make noise? What is normal

Some sounds are part of normal operation:

• Soft ticking as metal pipes and heat-trap nipples warm and cool
• A low hum from an electric element
• A gentle whoosh when a gas burner lights
• Gurgling right after heavy hot water use as the tank refills

These should be quiet and short. A change in volume or a new kind of sound is worth checking.

Tankless water heater noises

Tankless units click when they start and their fans hum. Those are normal. Rattling, banging or whistling can mean scale in the heat exchanger. Most makers call for regular descaling, and hard water makes it more urgent. A noisy tankless unit should be serviced, not ignored.

Why water heaters get noisy in Newark, DE

• Moderately hard water. WaterHardness.org lists Newark's city water at about 101 ppm, which counts as moderately hard. That is enough to build sediment over a few years.
• High temperature settings. The U.S. Department of Energy notes that lower settings slow mineral buildup and corrosion. Many tanks ship set near 140°F.
• Skipped flushing. A tank that has not been flushed in years may have more scale than one flush can remove.

How to prevent water heater noise

• Flush the tank once a year, or twice a year with harder water.
• Set the thermostat near 120°F. See our water heater temperature setting guide.
• Check the anode rod every few years.
• Keep house pressure under 80 psi.
• Add an expansion tank if your system is closed.

Local note: Popping and rumbling are common in Hockessin and Pike Creek homes with older gas tanks that have never been flushed. In Middletown, many newer homes have closed systems, so knocking during heating can point to expansion problems.

Related reading: If the noise comes with rust or leaks, read signs your water heater is going out. For age and life span, see how long do water heaters last?

When should you call a water heater professional?

Call a pro if:

• Popping or rumbling continues after a full flush
• You hear hissing with water near the burner or an element
• Banging happens while the heater runs, not just when taps close
• The relief valve whistles, drips or runs
• The tank is over 10 years old and getting louder

Water heater making noise in Newark? Call (302) 732-0874 for water heater maintenance from Newark Heater Pros.