Why does my water heater make popping noises?

That knocking or popping from the utility room is one of the most common calls we get, and it is almost never an emergency. It is also not nothing: the noise is a symptom of something that is quietly taking years off the tank.

What the noise actually is

Minerals in the water drop out of suspension when it is heated and settle on the bottom of the tank as a hard layer. Water gets trapped underneath that layer, turns to steam, and forces its way out. What you hear is the steam escaping through sediment, which is why it sounds like a kettle full of gravel.

Why it happens more here

Fairfax County water is moderately hard, and a good number of houses west of Route 28 are on wells that are harder still. More dissolved mineral means a thicker layer, sooner.

On a gas tank the sediment sits directly over the burner and insulates it from the water it is meant to be heating, so the burner runs longer and the steel above it runs hotter than it was designed for. On an electric tank it builds around the lower element and eventually buries it. Either way it is the bottom of the tank that suffers.

What a flush does and does not do

A yearly flush takes about forty minutes and genuinely adds years to a tank that has been kept up. On a tank that has gone a decade without one, a flush may only remove the loose material, and the hardened layer stays.

It is still worth doing. It is not worth doing repeatedly on a tank over twelve years old in the hope of avoiding a replacement.

When the noise means something else

A rhythmic banging that starts and stops with a tap or an appliance is not the heater at all, it is water hammer in the pipes. A high-pitched whistle is usually a valve partly closed somewhere.

And if the popping is new, loud, and paired with rusty hot water, do not schedule a flush. Get the tank looked at.

If your tank is under ten years old and popping, a flush is the right call. Over twelve, ask for an honest opinion before spending anything on it.