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How to flush a water heater

We'll flush sediment from the water heater to improve efficiency and extend its life.

How-to · Home plumbing
30–45 min
What you'll need
  • Garden hose (standard thread, 5/8 inch)
  • Bucket (if no floor drain)
  • Adjustable wrench (if the drain valve is stiff)

At a glance

  • Turn off the power or gas to the water heater before flushing—sediment can damage the heating elements or burner.
  • Attach a hose to the drain valve and run it to a floor drain or outside; open the valve and a hot faucet.
  • Let the tank drain until the water runs clear—or for at least 5 minutes if you have soft water.
  • Close the drain valve, refill the tank, and turn the power or gas back on.
  • Call a plumber if the drain valve is stuck, leaks, or will not close.
Quick triage — pick your path

Get started

Choose the option that matches what you see. You can jump straight to that section.

Steps

Goal: Flush sediment from the water heater safely.

  • Turn off the power or gas. Wait for the water to cool, or proceed with caution.
  • Good: Heater is off. Proceed to Shut off supply and attach hose.
  • Bad: Cannot locate the breaker or gas valve—call a plumber.

Shut off supply and attach hose

Goal: Prepare for draining.

  • Shut off the cold water supply. Attach a hose to the drain valve. Run the hose to a drain.
  • Good: Hose is secure. Proceed to Open drain and flush.
  • Bad: Drain valve is stuck—do not force; call a plumber.

Open drain and flush

Goal: Remove sediment from the tank.

  • Open a hot faucet. Open the drain valve. Let water run until clear or for at least 5 minutes.
  • Good: Water runs clear or significantly improved. Proceed to Close and refill.
  • Bad: No flow—drain valve may be clogged. Close and call a plumber.

Close and refill

Goal: Restore the tank to service.

  • Close the drain valve. Remove the hose. Turn the cold supply back on. Purge air at a hot faucet.
  • Good: Tank is full; no leaks. Proceed to Turn on and verify.
  • Bad: Drain valve leaks—tighten or replace; call a plumber if it will not seal.

Turn on and verify

Goal: Restore heat and confirm no leaks.

  • Turn the power or gas back on. Wait for hot water. Check the drain valve for leaks.
  • Good: Hot water at faucet; no leaks. Proceed to Verification.
  • Bad: Drain valve drips—see When to get help.

When to get help

Call a plumber if:

  • The drain valve is stuck and will not open or close.
  • The drain valve leaks after flushing and will not seal.
  • You have a tankless water heater—this guide is for tank units only.

Verification

  • No leaks at the drain valve after 30 minutes under pressure.
  • Hot water reaches the faucet at normal temperature.
  • Water may be slightly cloudy at first—run the hot faucet for a minute to clear it.

Reviewed by Blackbox Atlas

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