How to Flush Your Water Heater Tank
Sediment builds up inside every tank-style water heater. Over months and years, minerals from your water supply settle at the bottom, forming a layer that insulates the water from the burner, reduces efficiency, and eventually damages the tank. Flushing removes this sediment and is the single best thing you can do to extend the life of your water heater.
Time Required
30-45 minutes
Difficulty
Easy to Medium
Tools Needed
Garden hose, bucket
Hot Water Warning
The water inside your heater tank is at full temperature (typically 120-140°F). It will be extremely hot when it first comes out of the drain valve. Keep children and pets away. If possible, let the tank cool for an hour after turning off the heat source before draining. Always direct the hose to a safe location that can handle hot water — not onto a lawn or near plants.
Step 1: Turn Off the Heat Source
Gas water heaters
Turn the gas control valve to "Pilot" or "Off." The Pilot setting keeps the pilot light burning so you don't have to relight it later, but stops the burner from firing during the flush. If you choose Off, you'll need to relight the pilot afterward.
Electric water heaters
Flip the circuit breaker labeled "Water Heater" to the OFF position. This is essential — running an electric heating element in an empty or partially empty tank will burn out the element in minutes, which is a much more expensive repair than the flush itself.
Wait for the water to cool (optional but recommended)
If time allows, wait 1-2 hours after turning off the heat. This makes the draining process safer. If you're in a hurry, you can proceed immediately — just exercise extra caution with the hot water.
Step 2: Connect the Hose and Prepare to Drain
Attach a garden hose to the drain valve
The drain valve is at the bottom of the water heater tank. It looks like a hose bib (outdoor faucet). Thread a standard garden hose onto it. Make sure the connection is tight to prevent leaking during the drain.
Route the hose to a safe drain location
Run the other end of the hose to a floor drain, laundry sink, sump pit, or outdoors to a driveway or other hard surface. Remember, this water is hot and may be discolored with sediment — don't direct it onto plants, grass, or carpet.
Open a hot water faucet in the house
Turn on a hot water faucet at a sink or tub on an upper floor. This breaks the vacuum in the system and allows the tank to drain freely. Without this step, the tank drains extremely slowly or not at all — like putting your finger over a straw.
Step 3: Drain and Flush
Close the cold water inlet and open the drain valve
Turn off the cold water supply valve at the top of the heater. Then open the drain valve at the bottom. Water will begin flowing through the hose. A 40-50 gallon tank takes 15-20 minutes to drain completely. The water may be clear or rusty-brown — both are normal.
Flush the remaining sediment
After the tank is empty, briefly turn the cold water inlet back on for 15-20 seconds with the drain valve still open. This stirs up remaining sediment at the bottom and flushes it out through the hose. Repeat this 2-3 times until the water runs clear.
Check for drain valve clogs
If the flow slows to a trickle or stops during draining, sediment may be clogging the drain valve. Close the valve, disconnect the hose, and carefully insert a stiff wire or screwdriver into the valve opening to break up the blockage. Reconnect the hose and try again.
Step 4: Refill and Restore
Close the drain valve and disconnect the hose
Make sure the drain valve is fully closed. Remove the garden hose. Check for drips — if the drain valve leaks after closing, you may need to replace it (a common issue on older plastic drain valves).
Open the cold water supply fully
Turn the cold water inlet valve back on. Keep the hot water faucet you opened earlier running. You'll hear air sputtering from the faucet as the tank fills. Once water flows steadily from the faucet with no air bubbles, the tank is full. Close the faucet.
Restore the heat source
For gas heaters, turn the gas valve from "Pilot" back to "On" (or relight the pilot if you turned it off). For electric heaters, flip the breaker back on. Critical: Make sure the tank is completely full before restoring power to an electric heater. Running a heating element in an empty tank will destroy it.
Signs Your Tank Needs Flushing
- Popping or rumbling sounds: This is water boiling under a layer of sediment at the bottom of the tank. The sediment traps water pockets that turn to steam. This is the most common sign of significant buildup.
- Reduced hot water supply: If you're running out of hot water sooner than you used to, sediment is taking up space in the tank, reducing the volume of usable hot water.
- Longer heating times: Sediment insulates the water from the burner or heating element, making the heater work harder and longer to reach the set temperature. Your energy bills may be higher too.
- Rusty or discolored hot water: While some rust is normal in older tanks, a sudden increase in rusty or sandy-looking water often means sediment is being disturbed and carried to the faucets.
Pro Tips
- •Schedule it with another annual task: Pair your water heater flush with another annual chore like changing furnace filters or testing smoke detectors. This makes it easier to remember.
- •Upgrade to a brass drain valve: Many water heaters come with cheap plastic drain valves that leak or break easily. Replacing it with a brass ball valve ($10-$15) makes future flushes easier and eliminates a common leak point.
- •Check the anode rod while you're at it: Since you're already maintaining the water heater, this is a good time to inspect the sacrificial anode rod (the metal rod inside the tank that prevents corrosion). If it's more than 50% corroded, replace it to extend tank life.
- •Hard water areas need more frequent flushing: If you live in an area with hard water (common in the Southwest, Midwest, and Florida), flush every 6 months. You can test water hardness with a $5 test strip kit from any hardware store.
Frequently Asked Questions
How often should I flush my water heater?
Flush your water heater at least once per year. If you have hard water, flushing every 6 months is better. Hard water contains calcium and magnesium that settle at the bottom of the tank. Regular flushing prevents this buildup from reducing heating efficiency, causing noise, and shortening tank life.
What happens if I never flush my water heater?
Minerals settle at the bottom and form a thick sediment layer. This insulates water from the burner, forces the heater to work harder, causes rumbling noises, and leads to premature tank failure. Most water heaters that fail before their expected 8-12 year lifespan do so because of sediment buildup.
Can I flush a water heater that has never been flushed?
Yes, but proceed with caution. The drain valve may clog with sediment chunks. If flow stops, close and reopen the valve or use a stiff wire to clear it. On very old tanks that have never been flushed, there's a small risk of exposing weakened tank lining. If your tank is over 10 years old and never flushed, consider having a plumber assess it first.