How to flush a tank water heater
Turn off the power or set the gas to "pilot", close the cold-water supply, attach a hose to the drain valve, open a hot tap, and drain the tank until the water runs clear. Close the drain, refill completely (until water flows from the hot tap), then turn the heat back on. Most manufacturers call for it about once a year; check your manual.
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How to flush a tank water heater
Checklist
- Turn off power (electric) or set gas valve to pilotStep 1
- Close the cold-water supply valve on top of the tankStep 2
- Attach a hose to the drain valve and run it to a drain or outsideStep 3
- Open a hot faucet in the house, then open the drain valveStep 4
- Briefly open the cold supply to stir up sediment; repeat until clearStep 5
- Close the drain, open the cold supply, refill until the hot tap runs steadyStep 6
- Turn power or gas back on only after the tank is fullStep 7
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Safety first
The water is hot enough to scald; let it cool for a few hours or wear gloves. Never turn an electric water heater back on before the tank is full: the elements can burn out in seconds without water around them.
How often
Guidance ranges from every six months to once a year, and hard-water homes build sediment faster. Your heater's manual is the final word. If the drain valve is plastic and very old, it may leak after opening, so have a replacement or a cap handy.
What you'll need
- Water heater flush kit / drain hoseFits the drain valve and reaches a floor drain
- Brass drain valve (replaces an old plastic one)Old plastic valves often leak after use
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Questions
What happens if you never flush a water heater?
Sediment builds up on the bottom, which can make popping or rumbling noises, reduce efficiency, and shorten the tank's life.
How long does it take to flush a water heater?
About an hour for a typical 40–50 gallon tank, plus time to let the water cool first.
Related guides
General guidance for typical homes. Follow your equipment manufacturer's instructions and local codes, and hire a pro for anything you're not comfortable doing.