Why Is My Water Heater Popping Or Rumbling?

Water heaters are not silent, but they should not sound like a pot of popcorn. When a tank starts popping, rumbling, or hissing, the sound is usually telling you something specific, and in most Denver homes it is telling you about sediment.

This guide sorts the common noises by sound. If you are deciding whether a heater is worth keeping at all, our guide to the signs you need a new water heater covers repair versus replacement.

Noise By Noise: What You Are Hearing

Find the sound below, then read the likely cause and the next step.

Popping or rumbling

Likely cause: sediment. Minerals settle out of heated water and collect on the tank bottom. On a gas unit, the burner heats that layer from below, water trapped underneath boils, and steam bubbles push up through the sediment with a pop. On an electric unit, sediment buries the lower element and the water around it boils the same way.

What to do: a flush can clear loose sediment. On a tank that has been flushed regularly, that is a routine job. On a tank that has never been flushed, read the flushing section below first. Popping that continues after a proper flush usually means the sediment has hardened, which is a sign the tank is aging.

Crackling or sizzling

Likely cause: on a gas unit, condensation dripping onto the hot burner. It is most common when the tank refills with cold water, such as after heavy hot water use on a winter morning, and it usually fades as the tank warms. On an electric unit, a sizzle can come from scale on the heating element.

What to do: a condensation sizzle that comes and goes is normal. If the sizzling is constant, or you see water pooling under the burner area, have it checked, because that water may be coming from the tank rather than from condensation. A scaled electric element can be cleaned or replaced.

Ticking or tapping

Likely cause: pipes expanding and contracting as hot water starts and stops flowing, or the heat trap fittings at the top of the tank. Heat traps are small valves or loops that keep hot water from rising into the pipes when nobody is using it, and some types click as they open and close.

What to do: usually nothing. Ticking is a comfort issue, not a safety one. If it is loud, the fix is often a hanger that lets the pipe move without knocking against framing, or replacing a noisy heat trap.

Screeching or whistling

Likely cause: water forcing its way through a partially closed valve, most often the cold water inlet valve above the tank. A relief valve that is partly open can also whistle.

What to do: check that the inlet valve is fully open. If it is open and the noise continues, or the sound is coming from the relief valve, call a plumber. Do not force a corroded valve that will not turn.

Humming on electric units

Likely cause: a heating element that has worked loose, so water flowing past makes it vibrate. A faint hum is normal on many electric units.

What to do: a loud or new hum is worth having checked. Tightening or replacing an element means draining the tank and working near electrical connections, so turn the power off at the breaker and leave the repair to someone qualified. We hold both the plumbing and the electrical license for exactly this kind of work.

Hissing

Likely cause: one of three things, and they are not equally serious.

• Condensation on a gas burner. A brief sizzle and hiss as drops hit the flame, usually after a large draw of hot water. Normal, and it fades.
• The temperature and pressure relief valve. The valve on the side or top of the tank with a pipe running down toward the floor. If it is hissing, dripping, or discharging, the tank may be overheating or the system pressure may be too high.
• A leak. Water escaping from a fitting, the drain valve, or the tank itself.

How to tell which: look and feel. Condensation leaves no standing water and stops as the tank heats. A relief valve problem shows at the end of the discharge pipe, often as water on the floor or a drip from the pipe. A leak shows as moisture on the tank, the fittings, or the floor that keeps returning after you wipe it dry. If there is water on the floor or the relief valve is discharging, treat it as a stop and call situation.

Why Denver Tanks Get Loud

Denver water carries enough mineral content to matter over the life of a water heater. Every time the tank heats, some of those minerals settle out and land on the bottom. In a tank that is flushed regularly, the layer stays thin and loose. In a tank that is never flushed, which describes most of them, the layer thickens and hardens year after year.

That layer does more than make noise. Sediment insulates the burner from the water above it, so the burner runs longer to deliver the same hot water. The steel at the bottom of the tank runs hotter than it was designed to, which stresses the tank lining and shortens its life. Rumbling and slower recovery show up long before the tank fails. Our water heater service page covers the other local factors, including thermal expansion and the effect of altitude on gas units.

Flushing: When To Do It Yourself

Flushing means draining water out through the drain valve near the bottom of the tank, carrying loose sediment with it. On a heater that has been flushed regularly, it is a reasonable job for a careful homeowner.

On a tank that has never been flushed, be careful. Years of hardened sediment can clog the drain valve partway through, and an old drain valve may not reseat when you close it. That turns a maintenance task into a leak. If the heater is older and has never been serviced, have a plumber do the first flush. After that, an annual flush is easy to keep up.

If the popping stops after a flush, sediment was the cause. If it continues, the remaining layer is likely hardened onto the tank bottom, which flushing cannot remove. That is not an emergency, but it is a sign the tank is in the later part of its life, and the replacement signs are worth reviewing.

Tankless Units That Make Noise

A tankless water heater has no tank for sediment to settle in, but the same minerals build up as scale inside the heat exchanger. Scale makes the unit work harder, can cause a rattling or banging sound as water flashes against hot spots, and leads to error codes and swinging water temperature.

In hard water, annual descaling is required maintenance on a tankless unit rather than an optional service. Descaling circulates a mild acid solution through the heat exchanger to dissolve the buildup. Some sounds are normal at startup, such as fan noise and a click as the burner lights. A new or louder noise is the thing to watch for.

When The Noise Means Stop

Most of the sounds above can wait for a convenient appointment. A few cannot.

For anything else on this list, a noise is a symptom worth scheduling rather than ignoring. Our licensed plumbers repair and replace tank, tankless, and heat pump water heaters across Denver Metro, and if the noise turns out to be water escaping somewhere you cannot see, leak detection finds it.