Flushing removes the sediment that hard water leaves in the bottom of a tank. Sediment causes rumbling, slows heating and can shorten the life of the tank.
Safety first
Water in a tank can be scalding. Turn the heater off and let it cool for a few hours before draining, wear thick gloves and eye protection, and keep hands clear of the drain valve discharge.
How to drain and flush (A.O. Smith's steps)
- Turn off the power at the breaker (electric) or turn the gas control to off (gas).
- Close the cold-water inlet valve on top of the heater.
- Open a nearby hot-water faucet so air can enter and the tank can drain.
- Connect a garden hose to the drain valve and run it to a drain or outside.
- Open the drain valve and let the water run until it comes out clear.
- Close the drain valve, open the cold-water inlet and let the tank refill before turning the power or gas back on.
How often
Rheem recommends flushing once a year for most homes and every six months where water is hard. A.O. Smith says at least yearly, more often in hard-water areas. The City of San Diego reports its water averages about 16 grains per gallon of hardness, which is hard by any measure.
When to call a plumber
If the drain valve will not open, leaks or will not drain, Rheem and A.O. Smith both say to call a plumber or service technician. Turn the power or gas back on only after the tank is completely full again.
Common questions
How long does flushing take?
Usually under an hour, plus the time for the tank to cool beforehand and refill and reheat afterward.
What if the water never runs clear?
Heavy sediment may need repeated flushing. If it keeps coming, or the valve clogs, have a plumber look at it.
General information, not professional or legal advice; follow your manufacturer's manual, and your installer and local permit office have the final word. Sources:A.O. Smith, How to drain a water heater; A.O. Smith residential electric water heater manual (185762); Rheem, How often to flush your water heater; A.O. Smith, Water heater maintenance; City of San Diego, Water Quality (hardness).
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