How to flush a tank water heater

By Pau Cozar Navas · Last reviewed October 2026 · Checked against the official sources listed below

Flush a tank water heater at least once a year, which is what manufacturer A. O. Smith recommends for most models. If you have hard water, you may need to do it more often.

Unlike many home tasks, this one doesn't depend much on climate. Any time of year works, but picking the same month every year makes it easy to remember. The table below shows the month our home maintenance calendar suggests.

When to do it in your climate zone

Months are typical for each zone and match the free HouseByMonth calendar. Not sure of your zone? Find your climate zone. Weather varies year to year, so move a task earlier if a cold snap or heat wave arrives early.

Why flushing matters

Minerals in your water settle to the bottom of the tank as sediment. The U.S. Department of Energy notes that sediment impedes heat transfer and lowers the efficiency of the heater.

Flushing clears out that layer before it builds up. This guide covers tank (storage) water heaters. A. O. Smith notes that tankless units don't need flushing, though they may need descaling with a cleaning solution.

Lighter maintenance between flushes

You don't have to drain the whole tank every time. The Department of Energy suggests draining a quart of water from the tank every three months to remove sediment. University of Florida IFAS Extension gives a similar range of every three to six months.

Both sources also point to 120°F as a good temperature setting. The Department of Energy describes it as safe for most of the population.

Is it time to flush?

These clues suggest sediment has built up:

• Rumbling or popping sounds from the tank while it heats.
• Cloudy or gritty hot water, or flakes in faucet aerators.
• You live in an area with hard water.
• You don't know when the tank was last flushed.

Before you start

Read the manual for your model first. UF IFAS Extension advises checking the manufacturer's instructions before any maintenance, because drain valves and controls vary.

You'll need a garden hose long enough to reach a floor drain or the outdoors, and a bucket for checking the water. Plan for the job to take a while, since the tank needs time to cool.

How to flush a water heater, step by step

1. Turn off the heat source. For an electric heater, A. O. Smith says to switch off its circuit breaker. For a gas heater, turn the thermostat dial to off, or to pilot as Bradford White instructs.
2. Let the water cool for a few hours before draining to reduce the risk of scalds.
3. Shut off the cold water supply valve on the pipe feeding the tank. If there isn't one, use your home's main shut-off valve.
4. Attach a garden hose to the drain valve near the bottom of the tank. Run the other end to a floor drain or outside, somewhere hot water won't cause damage.
5. Open a hot water faucet in the house. This keeps pressure from building up in the plumbing.
6. Open the drain valve and let the tank empty. Watch the water for sediment. Bradford White's instructions open the pressure relief valve at this point to help the tank drain completely. Water can come out of the relief valve's discharge pipe, so keep clear of its outlet.
7. To rinse out remaining sediment, Energy Trust of Oregon suggests turning the cold water supply back on with the hose still attached. Let it run until the water from the hose runs clear.
8. Close the drain valve, remove the hose, and close the relief valve if you opened it.
9. Refill the tank. Open the hot water faucets in the house, then turn on the cold water inlet. Close each faucet once water flows steadily from it.
10. Only after the tank is full, restore the heat. Turn the breaker back on, or set the gas control back to on and relight the pilot following the manufacturer's instructions.

Check the drain valve for drips over the next day. A slow leak that doesn't stop after closing the valve firmly may mean the valve needs replacing.

Scalding and gas safety

The water in the tank can be scalding. Let it cool first, and keep hands and the hose outlet away from where water discharges.

Never turn the power or gas back on before the tank is completely full. That is why every manufacturer sequence above refills the tank first.

If you smell gas at any point, don't switch lights or appliances on or off and don't try to shut off the gas. Leave the house and call 911 or your gas company from outside.

When to hand it to a plumber

Bradford White recommends having a plumbing professional help with maintenance, even though some simple checks are DIY. Call one if the drain valve won't open, won't close or breaks, or if the tank won't drain because of heavy sediment.

Also call a pro if the pressure relief valve leaks after you close it, or if you're not comfortable relighting a gas pilot. Any repair to gas lines or venting belongs with a licensed plumber or gas technician.

While you are in the utility room

Your water heater is often next to the furnace, so it's a good moment to check the air filter. See how often to change your HVAC filter for that schedule.

Gas water heaters and furnaces both burn fuel, which makes working carbon monoxide alarms important. The guide to smoke and CO alarm maintenance explains how to test them.

Sources

• A. O. Smith: How to drain and flush a water heater
• Bradford White: Draining a water heater
• U.S. Department of Energy: Energy Saver guide (2022)
• Energy Trust of Oregon: Drain, flush and save
• University of Florida IFAS Extension: Energy efficient homes, water heaters
• Mass.gov: What to do if you smell gas