Flush water heater

Drain and flush your water heater tank to remove sediment buildup that accumulates over time from minerals in your water supply.

Why it matters#

Sediment buildup creates an insulating layer between the heat source and your water, forcing your heater to work harder and driving up energy costs. On gas heaters, sediment creates hot spots that can damage the tank and cause premature failure. On electric heaters, it can bury and burn out the lower heating element. Annual flushing extends your water heater's lifespan by years and can save you from a $3,500+ replacement.

What you'll need#

Tools#

• Garden hose
• Adjustable wrench
• Flathead screwdriver
• Bucket or floor drain access

Materials#

• Replacement drain valve for severely clogged units (optional)

Safety gear#

• Heat-resistant gloves
• Safety glasses
• Closed-toe shoes

Steps#

1. Turn Off the Power Source#

For electric water heaters, flip the dedicated circuit breaker OFF at your main electrical panel. For gas heaters, turn the gas valve to "Pilot" or "Off" position. This is critical—running an electric heating element without water will burn it out immediately.

2. Let the Water Cool#

Open a hot water faucet somewhere in the house and let it run full blast for about 10 minutes. This reduces the water temperature in the tank and makes the job safer. Alternatively, you can wait several hours after turning off power for the water to cool naturally.

3. Shut Off the Cold Water Supply#

Locate and close the cold water supply valve at the top of the tank. This prevents new water from entering during the flush.

4. Connect the Hose and Open Pressure Relief#

Attach a standard garden hose to the drain valve near the bottom of the tank. Route the hose to a floor drain, bucket, or outside—the water will be hot and contain sediment. Open the temperature-pressure relief (T&P) valve at the top to break the vacuum and allow water to flow freely.

5. Open the Drain Valve and Let It Flow#

Open the drain valve fully using the handle or a flathead screwdriver. Let the tank drain completely—this takes 15-20 minutes for a standard 40-50 gallon tank. Watch the initial water; if it's cloudy or sandy, you have significant sediment buildup.

6. Flush with Cold Water Bursts#

With the drain valve still open, briefly turn on the cold water supply valve for 10-15 second bursts. This blast of fresh water agitates and stirs up stubborn sediment stuck at the bottom. Repeat 3-4 times until the water runs clear.

7. Close Up and Refill#

Close the drain valve, disconnect the hose, and close the T&P valve. Open the cold water supply fully to refill the tank. Open a hot water faucet upstairs and let it run—when water flows steadily (not sputtering air), the tank is full.

8. Restore Power#

For electric heaters, flip the breaker back ON only after the tank is completely full. For gas heaters, turn the gas valve to "On" and relight the pilot if necessary. Wait 30-60 minutes for the water to heat up before using.

Pro tips#

• Place a kitchen colander over the floor drain or hose end to catch sediment—this prevents clogging your drain and shows you exactly how much buildup you're removing.
• If you hear popping or rumbling sounds from your water heater, that's steam bubbles percolating through sediment—it's past time to flush.
• In hard water areas, flush every 6 months instead of annually; you'll notice the difference in your energy bills.

Warnings#

• The water draining from your tank will be VERY HOT (120-140°F). Wear gloves and keep children and pets away from the hose outlet.
• Never turn on an electric water heater's power until the tank is completely full—"dry firing" will destroy the heating element immediately and may void your warranty.
• If your water heater is old and has never been flushed, proceed with caution. Disturbing years of sediment can sometimes dislodge buildup that was actually helping seal small corroded areas, potentially causing leaks.

When to call a pro#

If the drain valve is completely clogged and won't open, or if you notice significant rust-colored water or the tank has never been flushed and is over 6 years old, have a professional assess the situation. They can replace corroded drain valves and check for tank damage that might make flushing risky.