How to Flush a Water Heater Tank

Why Flushing Is Important

Minerals in your water supply settle to the bottom of your water heater tank over time, forming a layer of sediment. This sediment insulates the water from the burner (in gas heaters) or heating elements (in electric heaters), forcing the unit to work harder and use more energy. Sediment also causes popping or rumbling noises during heating cycles and can clog the drain valve. Annual flushing extends the life of your water heater and maintains its efficiency.

Preparation Steps

Turn off the gas valve or electrical breaker supplying your water heater. Close the cold water inlet valve on top of the heater. Attach a garden hose to the drain valve near the bottom of the tank and run the hose to a floor drain, outside, or into buckets. Let the water cool for at least an hour to avoid scalding — water heater temperature typically exceeds 120 degrees Fahrenheit. Open a hot water faucet in your home to allow air into the system and facilitate draining.

Flushing Procedure

Open the drain valve and let water flow through the hose. The first water out will likely be cloudy with sediment. Allow the tank to drain completely, then briefly open and close the cold water inlet valve several times in short bursts to stir up remaining sediment on the tank bottom. Continue flushing until the water runs clear. If the drain valve clogs with sediment, close it briefly and reopen, or use a long screwdriver to carefully dislodge debris from the valve opening.

Refilling and Restarting

Close the drain valve and remove the hose. Open the cold water inlet valve fully and wait for the tank to fill completely — you will know it is full when the hot water faucet you opened earlier runs a steady stream without sputtering. Close the hot water faucet. For gas heaters, relight the pilot or turn the gas valve to the on position. For electric heaters, turn on the circuit breaker only after confirming the tank is completely full — energizing heating elements in an empty tank will burn them out immediately.