How often should you flush a water heater?

The short answer: once a year for a tank water heater. The longer answer depends on your water, your heater and how hard it works.

What builds up in the tank

Water carries tiny amounts of minerals and grit. When it is heated, some of that drops out and settles at the bottom of the tank. Over the years it builds into a layer of sediment between the burner or element and the water you want hot.

That layer does three things. The heater has to run longer to heat the same water, so it costs more to run. The sediment traps steam bubbles, which is the rumbling or popping you may hear. And it takes up room, so you get less hot water before it runs out.

Portland water and sediment

Portland's own water is soft, so homes on city water usually build up sediment slowly. Some of the suburbs get water from other sources, and a house on a well can have much more mineral in it. Soft water does not mean you can skip it altogether: grit from the mains, and the anode rod slowly wearing away, still end up in the bottom of the tank.

Signs yours is overdue

• Rumbling, popping or crackling when the heater runs
• Hot water running out sooner than it used to
• Cloudy, sandy or rusty-looking hot water
• A heater that has never been flushed and is more than a few years old

Why we check the anode rod at the same time

The anode rod is a metal rod inside the tank that corrodes so the tank doesn't. Once it is used up, the tank itself starts to rust, and a rusted tank is a leaking tank sooner or later. Checking it while the heater is drained costs nothing extra in time, and replacing a worn rod can add years to a heater.

Can you do it yourself?

You can, if you are comfortable shutting off the gas or power, connecting a hose to the drain valve and running scalding water somewhere safe. The catch is an old drain valve that won't close properly once it has been opened, or a tank so full of sediment the valve clogs. If your heater is more than about eight years old and has never been flushed, have a technician do the first one.

Tankless heaters are different

A tankless heater has no tank to flush, but mineral scale can build up inside its heat exchanger. Most makers recommend descaling it once a year, and more often with harder water. The manual for your model will say.