How to flush a tank water heater

Why flushing matters

Minerals in the water settle at the bottom of the tank as sediment. Over time it insulates the water from the burner or element, so the heater works harder, makes popping or rumbling noises, and wears out sooner. A yearly flush keeps the buildup under control.

Before you start

• The water in the tank is hot enough to scald. Let it cool for a few hours, or take extra care.
• You’ll need a garden hose long enough to reach a drain, the driveway or the yard.
• Know where the cold water shutoff is, on the pipe at the top of the heater.

Tip: If your heater has a plastic drain valve and hasn’t been flushed in years, the valve can crack or refuse to close. If you’re unsure, have a plumber do the first flush.

Step by step

1. Turn off the heatGas: set the control dial to “Pilot” or “Vacation.” Electric: switch off the breaker for the water heater.
2. Shut off the cold water supplyClose the valve on the cold water line at the top of the heater.
3. Connect a hose to the drain valveRun the other end somewhere hot water won’t cause damage, like a floor drain or the driveway.
4. Open a hot water faucetOpen a hot faucet in the house to let air in so the tank drains smoothly.
5. Open the drain valveLet the tank drain. The first water out will be cloudy with sediment.
6. Flush with fresh waterWith the drain still open, briefly open the cold supply to stir up and rinse out the remaining sediment. Repeat until the water runs clear.
7. Close the drain and refillClose the drain valve, remove the hose and open the cold supply. Leave the hot faucet open until water flows steadily with no sputtering, which means the tank is full.
8. Turn the heat back onGas: return the dial to its normal setting. Electric: switch the breaker back on, but only once the tank is completely full.

When to call a plumber

• The drain valve won’t open, won’t close, or leaks after flushing.
• The heater is over 10 years old and has never been flushed.
• You still hear popping after flushing.
• The water is still rusty or smells bad.
• You have a tankless heater, which needs a pump and descaling solution instead.

How often to flush

Once a year is a good rule in most Los Angeles homes. If your water is especially hard or you notice popping sounds, every six months can help.