How to Flush a Water Heater
Updated February 20, 2026
Drain sediment from your water heater tank to restore heating efficiency, reduce noise, and extend the unit's lifespan. 30-minute annual maintenance task.
Overview
Sediment builds up in every tank water heater. Dissolved minerals precipitate out of heated water and settle on the bottom. Gas heaters: sediment insulates the tank from the burner, wasting energy and overheating the tank floor. Electric heaters: sediment buries the lower element, causing it to overheat and burn out. Both types get noisy -- popping, rumbling, crackling. Flushing takes 30 minutes, costs nothing, and is the single most important maintenance task for any tank water heater. Do it once a year.
What You'll Need
Safety First
- Water in the tank is hot -- up to 140 degrees. Let it cool for several hours before draining, or handle the hose discharge carefully.
- Never stand directly in front of the drain valve when opening it. Sediment chunks can cause intermittent pressure spurts.
Step-by-Step Instructions
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Turn Off the Heat Source
Gas heater: turn the gas valve to PILOT or OFF. Electric heater: turn off the breaker at the panel. Do not skip this -- heating an empty or partially empty tank damages it. Gas tanks with the burner firing and no water can warp the tank floor. Electric elements burn out in minutes without water.
Tip: If you want to drain hot water (faster but riskier), you can leave the heat on until you start draining, then shut it off. But letting it cool first is safer. -
Connect a Garden Hose to the Drain Valve
The drain valve is at the bottom of the tank -- looks like a hose bib. Connect a standard garden hose. Run the other end to a floor drain, outside, or into buckets. Make sure the hose end is lower than the valve for gravity drainage. If running outside, keep it away from plants -- hot sediment water can kill them.
Tip: Plastic drain valves on cheaper water heaters are prone to leaking and breaking. If yours looks fragile, do not force it. A brass replacement valve ($8-12) is a worthwhile upgrade. -
Open the Drain Valve and a Hot Water Tap
Open a hot water faucet upstairs or nearby -- this breaks the vacuum in the tank and lets it drain freely. Then open the drain valve. Water will flow through the hose. It will likely be discolored -- rusty, cloudy, or sandy depending on how much sediment has accumulated. Let the tank drain completely.
Tip: If water flow slows to a trickle, sediment may be clogging the drain valve. Close the valve, disconnect the hose briefly, and use a long screwdriver to break up the sediment blocking the opening. Reconnect and continue. -
Flush Until Clear
With the tank empty, briefly turn the cold water supply on and off in 15-second bursts. This stirs up remaining sediment on the tank bottom and flushes it out through the drain. Watch the hose discharge -- repeat until the water runs clear. Three to five flushes usually does it. Heavily neglected tanks may take more.
Tip: If the water never runs clear or you see large chunks of calcium, the tank may have years of buildup. Keep flushing. If the drain valve clogs repeatedly, the tank may need professional descaling or replacement. -
Close Up and Refill
Close the drain valve. Disconnect the hose. Leave the hot water faucet upstairs open. Turn the cold water supply fully on. The tank will fill -- you will hear it. When water flows steadily from the open hot faucet (no air sputtering), the tank is full. Close the faucet.
Tip: Let the water run from the faucet for a minute after the air clears. This flushes any loose sediment that made it into the hot water pipes during draining. -
Restore Power and Verify
Gas heater: turn the gas valve back to ON and relight the pilot if needed. Electric heater: turn the breaker back on. Wait 30-60 minutes, then check for hot water at a faucet. Check the drain valve for drips -- tighten slightly or cap with a brass cap if it seeps.
Tip: If the drain valve leaks after closing, attach a brass hose cap to the end. Replacement drain valves are easy to install while the tank is empty if you catch it during the flush.
Pro Tips
- Flush annually. Mark it on the calendar. Every year of skipped flushing adds another layer of sediment that reduces capacity and efficiency.
- If your water heater is more than 5 years old and has never been flushed, go slowly. Heavy sediment can clog the drain valve. Have a brass cap ready in case the valve will not fully close afterward.
- Hard water areas need flushing every 6 months instead of annually. If you see heavy sediment each time, increase frequency.
- While the tank is drained, test the T&P (temperature and pressure) relief valve. Lift the lever briefly -- water should discharge and stop when you release. If it keeps running or will not lift, replace the valve.
- Consider installing a powered anode rod ($50-100) which actively fights sediment and corrosion instead of just sacrificing like a standard anode.
When to Call a Pro
Flushing is always DIY. But if the drain valve is stuck and will not open, if the drain valve breaks or will not stop leaking after closing, if the tank is so full of sediment that flushing will not clear it, or if the T&P valve is stuck or leaking, call a plumber. A tank that has never been flushed in 10+ years may not be worth flushing -- the sediment may be the only thing holding it together.