How to Flush Your Water Heater

Your water heater quietly does its job year after year, heating water for showers, dishes, and laundry. But inside that tank, something is slowly building up. Sediment—minerals from your water—settles to the bottom and accumulates. Over time, this layer of gunk makes your heater less efficient, noisier, and closer to failure. Flushing removes that sediment.

Why This Matters

Sediment buildup is the number one cause of water heater problems:

• Reduced efficiency – Sediment insulates the water from the heat source
• Higher energy costs – More energy needed to heat the same amount of water
• Rumbling and popping noises – Water trapped under sediment boils and bursts through
• Overheating damage – The tank bottom gets too hot
• Shortened lifespan – Most water heaters fail from sediment-related problems
• Reduced capacity – Sediment takes up space that should hold water
• Eventual leaks – Overheating weakens the tank

A water heater that should last 12-15 years might fail in 8 if never flushed. The fix is simple and costs nothing but time.

Understanding Sediment

All water contains dissolved minerals—calcium, magnesium, and others. When water is heated:

1. Minerals precipitate out and form solid particles
2. These particles are heavier than water and settle to the bottom
3. They accumulate into a layer of scale
4. The scale hardens over time

Hard water (high mineral content) produces more sediment. Soft water produces less, but some minerals still accumulate.

Step-by-Step Flushing Process

Step 1: Turn Off the Power

This is critical for safety and to protect the heater:

Electric Water Heaters:

1. Find the breaker for the water heater
2. Turn it OFF
3. Verify it’s the right breaker

Gas Water Heaters:

1. Find the temperature dial on the gas control valve
2. Turn it to “Pilot” or “Vacation” mode
3. The pilot stays lit but the main burner won’t fire

Step 2: Turn Off the Cold Water Supply

1. Locate the cold water pipe entering the top of the tank
2. Find the shutoff valve on this pipe
3. Turn it OFF (handle perpendicular to the pipe)

Step 3: Let the Water Cool

The water inside is 120°F or hotter—hot enough to cause burns. Let it cool for at least 1-2 hours before draining. The tank is insulated and holds heat well.

Step 4: Connect a Drain Hose

1. Find the drain valve at the bottom of the tank
2. Screw on a garden hose
3. Run the other end to a floor drain, outside, or into buckets
4. Place towels around the valve—these often drip

Step 5: Open a Hot Water Faucet

1. Go to a nearby faucet or tub
2. Turn on the hot water side
3. This allows air into the tank so it can drain

Step 6: Open the Drain Valve

1. Open the valve slowly
2. The water will start flowing out
3. Let it drain completely
4. The first water out will be the dirtiest

Step 7: Flush with Fresh Water

This is the actual “flushing” part:

1. Turn the cold water supply back ON
2. Let it run into the tank for 30-60 seconds
3. This stirs up remaining sediment
4. Watch the water coming out of the hose
5. Turn cold water OFF and let drain again
6. Repeat until the water runs clear

You may need to do this 3-5 times for a tank that hasn’t been flushed in a while.

Step 8: Close the Drain Valve

1. Once water runs clear, close the drain valve tightly
2. Remove the hose
3. Have a bucket ready for residual water in the hose

Step 9: Refill Before Restoring Power

This is critical for electric heaters:

1. Make sure the drain valve is closed
2. Turn on the cold water supply
3. Wait for the tank to fill completely
4. You’ll know it’s full when water flows from the open hot tap
5. Turn off that faucet
6. NOW you can restore power

Never turn on power to an electric water heater that isn’t full of water. The heating element will burn out in seconds.

Step 10: Restore Power

Electric: Turn the breaker back on Gas: Turn the dial back to the desired temperature setting

What If the Drain Valve Is Clogged?

On older heaters, sediment can clog the drain valve itself:

1. Try opening and closing it several times
2. The water pressure might clear it
3. If not, you can try removing the valve and using a wire to clear the opening
4. This requires draining the tank first and having a replacement valve ready

Tankless Water Heaters

Tankless units need flushing too, but the process is different:

1. They require a specific flushing kit with a pump
2. Vinegar or a descaling solution circulates through the unit
3. Follow the manufacturer’s instructions

If you have a tankless unit, consider professional maintenance.

DIY vs. Call a Pro

DIY: Regular annual flushing on tank water heaters in good condition.

Call a pro: Heaters that haven’t been flushed in many years, stuck drain valves, leaks, or tankless systems. Find a plumber →

How Often to Flush

• Hard water areas: Every 6 months
• Average water: Once a year
• Soft water: Once a year minimum
• If you hear rumbling: As soon as possible

The Bottom Line

Flushing your water heater is the single most important maintenance you can do for it. It costs nothing but an hour or two of your time. It extends the life of the tank, improves efficiency, and prevents the rumbling noises that tell you something is wrong. Do it once a year, every year.