How to Flush Your Water Heater Tank and Remove Sediment Buildup
Safety Warning
Water heater tanks contain extremely hot water (typically 120-140°F) that can cause severe burns. Turn off the power (electric) or gas supply before starting, and let the water cool for several hours if possible. Do not attempt to flush if you smell rotten eggs or have a leaking tank, as this indicates serious problems requiring professional service. If your water heater is older than 12 years, has visible rust, or shows signs of leaking, contact a professional plumber instead of attempting this task yourself.
Sediment accumulation inside your water heater reduces efficiency by up to 25% and can shorten your tank's lifespan by 5 years or more, potentially costing you $1,200-2,500 in premature replacement. Flushing your water heater annually is a straightforward DIY task that any homeowner can complete in about an hour with basic tools. This simple maintenance task will help your water heater operate efficiently, reduce energy bills, and extend its life significantly.
What You'll Need
Supplies
- •Garden hose or drain hose (25-50 feet)($15-30)
- •Plumber's tape (PTFE thread seal tape)(optional)($3-5)
- •Penetrating oil (WD-40 or similar)(optional)($5-8)
Tools
- •Adjustable wrench or pipe wrench
- •Bucket (5-gallon for catching water)
- •Flashlight or headlamp(optional)
- •Thermometer (optional, to verify water temperature)(optional)
Step-by-Step Instructions
Turn off the power or gas supply to the water heater
Locate the power switch for electric water heaters or the gas valve knob for gas models. For electric heaters, switch the breaker to OFF at your electrical panel. For gas heaters, turn the dial to the PILOT position or fully OFF if instructed by your manual. Wait at least 2-3 hours for the water to cool to a safe temperature before proceeding.
Pro Tip: If you have a tankless water heater or heat pump model, consult your manual as these systems may have different flushing procedures or may not require flushing.
Turn off the cold water supply valve to the tank
Locate the cold water inlet valve on top of your water heater—it should have a handle or lever. Turn this valve clockwise (or move the lever to a perpendicular position) to stop cold water from entering the tank. Once closed, try to open a hot water tap in your home to confirm the water supply is shut off; only a small amount of water should come out.
Pro Tip: If the valve is stuck or will not turn, apply a penetrating oil like WD-40 and wait 15 minutes before trying again.
Attach a drain hose to the drain valve at the bottom of the tank
Locate the drain valve at the lowest point of the water heater tank—it looks like a small outdoor faucet. Attach one end of your drain hose (garden hose works well) to this valve by turning the hose connector clockwise onto the valve threads. Direct the other end of the hose to a floor drain, utility sink, or outside location where hot water can safely drain (avoid gardens or pet areas due to mineral content).
Pro Tip: If the drain valve is difficult to access, you may need to move items stored near your water heater first. Ensure the hose has no kinks that would block water flow.
Open the drain valve to begin draining the tank
Turn the drain valve knob counterclockwise to open it fully. You should hear water beginning to flow through the hose. The water may come out brown, cloudy, or dark due to sediment—this is normal. Let the tank drain completely; this process typically takes 15-30 minutes depending on tank size and sediment buildup.
Pro Tip: Place a bucket under the hose connection near the valve to catch any water that drips after closing the valve later.
Open a hot water faucet inside your home to allow air into the tank
Go to any sink in your home and turn on the hot water tap fully. This allows air to enter the tank as it drains, which prevents a vacuum from forming and speeds up the draining process. Leave this faucet open until the water stops flowing and only air comes out.
Pro Tip: Doing this step prevents incomplete draining and makes the subsequent refill process smoother.
Flush the tank by opening the cold water valve briefly
Once the tank has drained completely and the hot water faucet has stopped flowing, turn the cold water inlet valve back on for 30-60 seconds, then immediately turn it off again. This sends fresh water into the bottom of the tank, which stirs up and flushes out remaining sediment through the drain valve. You should see dirty water flowing out again; repeat this flushing action 2-3 times until the water runs relatively clear.
Pro Tip: If sediment is heavy, you may need to repeat the flush-and-drain cycle up to 5 times for best results.
Close the drain valve and remove the hose
Once the water runs clear and you are satisfied with the flushing, turn the drain valve knob clockwise to close it completely. Wait for any remaining water in the hose to drain into your bucket, then unscrew and disconnect the drain hose from the valve. Ensure the valve is fully closed by trying to turn it slightly more—it should stop with firm resistance, not hand-tightness.
Pro Tip: Wrap the drain valve threads with plumber's tape before reconnecting the hose in future years to prevent leaks.
Refill the tank and restore power
Turn the cold water inlet valve back on by turning the handle counterclockwise (or moving the lever to align with the pipe). Listen as the tank refills—you will hear rushing water sounds for several minutes. Go back inside and turn off the hot water faucet you opened earlier once water flows steadily. After the tank has refilled (5-10 minutes), turn the power or gas back on, and check that hot water flows normally at your faucets within 10-15 minutes.
Pro Tip: If you have an electric water heater, set the temperature dial back to your preferred setting (usually 120°F) after restoring power.
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