For a healthy water heater, you should flush it every year. Over time, sediments such as minerals and debris accumulate in the tank. They can pile up into a solid concrete-like mass and cause all sorts of problems: they're corrosive and can eat through the tank and cause a leak, they cause temperature fluctuations, they clog the drain, they make the heater noisy, they raise your energy bills, and they can eventually cause the unit to fail.
To avoid all of that, flush your water heater every year. Flushing means emptying the tank and then agitating the accumulated sediment so it can be washed out. It's simple, you can do it yourself, and it can save you more than $100 every year.
Step 1: Turn Off the Power Supply
Gas: Turn the temperature control dial on the lower side of the tank to off or to the pilot setting. Electric: Go to your breaker panel and switch off the water-heater breaker. If you don't turn off the power, you risk heating an empty tank once it's drained, which can ruin the unit.
Step 2: Turn Off the Cold Water Supply
At the top of the heater you'll find two pipes, one with a valve. Rotate that valve until it's perpendicular to the pipe to shut off incoming cold water.
Step 3: Connect a Hose
Attach one end of a garden hose to the drain spigot near the bottom of the tank and put the other end in a bucket so you can inspect the water and avoid spillage. Open the drain valve — don't be surprised if water doesn't flow immediately, because the tank needs air to drain.
Step 4: Open a Hot Water Faucet
Open a hot water faucet somewhere in the house so air can enter the system — otherwise the tank acts like a straw with your finger over the end and nothing drains.
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Step 5: Open the Drain Valve
Turn the drain valve handle parallel to the hose (or use a flat-head screwdriver on the screw-head). If you hear no water or air movement, you may have a backflow preventer in your plumbing — in that case you'll need to open the pressure relief valve to admit air.
Step 6: Open the Pressure Relief Valve
The relief valve is a safety device at the top of the tank. Lift the lever (place a bucket underneath first in case water comes out). You should immediately hear air rushing in and water flowing out the drain below.
Step 7: Inspect the Draining Water
Let the tank drain for 15–20 minutes and inspect the water. If nothing drains, the drain valve may be clogged with sediment — blow into the hose once or twice to push the scale back. If water still won't come, the sediment may be blocking the valve and you'll need a plumber. Caution: draining water is scalding — keep children and pets away.
Step 8: Flush in Bursts
Draining alone is gentle and won't dislodge much sediment. Empty the bucket, then briefly open the cold water supply for 15–20 seconds to agitate the sediment at the bottom, then close it and let the tank drain again. Inspect the bucket for debris and repeat until the water runs clear.
Step 9: Restart the Water Heater
Close the drain valve and remove the hose. Open the cold water supply and let the tank fill until it's about half full, then close the relief valve by pushing the lever down. Set the thermostat back to your desired temperature, and finally open a hot water faucet to let air out of the lines. Once the water flows smoothly, close the faucet — you've flushed your water heater like a professional.