How to Flush a Water Heater Tank

Before you start

Water in Peel Region is moderately hard, so dissolved minerals precipitate inside heated tanks. Over the years that sediment forms a layer that insulates the water from the burner or elements, causing rumbling noises and longer heating times.

• A length of hose that can reach the floor drain or a door
• A flat-blade screwdriver or wrench for the drain valve, depending on its style
• A bucket for checking the water
• Gloves, since the water will be hot

Step by step

1. Turn off the heat. Turn a gas unit's dial to pilot or off, or open the breaker feeding an electric one.
2. Close the cold supply. Shut the valve on the cold-water inlet above the tank.
3. Connect the hose. Attach it to the drain valve near the base and run the other end to a floor drain.
4. Open a hot tap. A nearby hot-water faucet lets air in so the tank drains freely.
5. Open the drain valve. Let the tank empty. Expect cloudy or gritty water at first.
6. Stir the sediment. Briefly open the cold supply with the drain still open to agitate the bottom, then close it again.
7. Refill completely. Close the drain, open the cold supply, and wait until the hot tap runs steadily without sputtering.
8. Restore heat. Only once the tank is full, relight the gas or switch the breaker back on.

Mistakes to avoid

• Powering an empty electric tank. The elements burn out almost immediately without water around them.
• Forcing a plastic drain valve. These can crack; open them gently.
• Skipping years. A tank never flushed in a decade may have so much sediment that the valve clogs.
• Leaving the drain dripping. Check it again after an hour.

Checking the anode rod

Inside most tanks hangs an anode rod, designed to corrode so the steel shell does not. Once it is consumed, the tank itself begins to rust. Inspecting the rod every few years is a sensible addition to flushing, although the hex fitting on top of the tank is often very tight and requires a large socket and considerable force. If you would rather not attempt it, we can check the rod during a service visit and tell you whether replacement is due.

When to call

If the drain valve leaks after closing, the water never runs clear, or the tank is rusty at its fittings, call for help. Ongoing heating problems may need water heater repair, and old tanks are worth reviewing against our guide on when to replace a water heater. Tankless units follow a different process covered under tankless descaling. While you are in the basement, consider testing your sump pump as well.

Worth knowing

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