How often should you flush your water heater tank?

Sediment buildup wastes energy and shortens tank life.

Sediment insulates the water from the heat source, so the heater runs longer for the same hot water. It also causes the popping and rumbling sound that A. O. Smith lists as a sign a tank needs flushing. The US Centers for Disease Control and Prevention says regular flushing helps a water heater last longer and helps stop germs growing in it.

1. Turn off the heat source. Gas to Pilot, or the breaker off for electric. Never drain an electric tank with the elements powered.
2. Shut the cold inlet and let it cool. A. O. Smith suggests turning the heater off for a few hours before draining, so the water cools and the risk of scalds drops. Wear thick gloves and eye protection.
3. Attach a hose to the drain valve. Run it to a floor drain or outside, somewhere downhill from the tank.
4. Open a hot tap upstairs. This breaks the vacuum so the tank actually drains rather than gurgling.
5. Open the drain valve and empty the tank. Expect discoloured water and grit. Keep going until it runs clear.
6. Flush with short bursts of cold. With the drain still open, briefly open the cold inlet a few times to stir and carry out the remaining sediment, until no more comes out.
7. Close, refill, then restore heat. Close the drain, refill fully, and only restore gas or power once water runs steadily from the open tap with no air.

• Popping, rumbling or kettling sounds as the heater runs
• Hot water running out sooner than it used to
• Discoloured or gritty water from hot taps
• The heater taking noticeably longer to recover between showers

• Draining an electric tank with the breaker still on, or restoring power before the tank is full: an element that is not covered by water burns out
• Forgetting to open a hot tap, then wondering why nothing drains
• Ignoring the anode rod, the sacrificial part that protects the tank from corrosion: A. O. Smith recommends inspecting it once a year
• Opening a drain valve on a very old tank that has never been flushed: heavy sediment can prevent it closing again, so be ready for that

• A. O. Smith says most tank water heaters need flushing at least once a year, and more often in hard water areas
• Tankless heaters have no tank to flush but many need descaling, and the interval depends on the model and the water
• Softened water leaves less sediment, but a softener changes how quickly the anode rod is used up, so the rod still needs its check

If the drain valve will not close afterwards, if the tank is leaking from the body rather than a fitting, or if the relief valve discharges, call a plumber. A tank leaking from its body usually means a replacement. A. O. Smith also recommends having a professional examine the temperature and pressure relief valve every five years.