How to Flush a Water Heater (Step-by-Step) — Tank & Tankless

Sediment — minerals and grit that settle out of your water — slowly builds up at the bottom of a water heater tank. Left alone it wastes energy, makes the tank noisy, and shortens its life. Flushing the tank once a year clears that sediment out, and it's a job most homeowners can do with a garden hose in under an hour. Here's how to do it safely.

Why flushing matters

As water is heated, dissolved minerals (especially in hard water) drop out and collect at the bottom of the tank. That layer of sediment causes real problems:

• On a gas heater, it sits between the burner and the water, so the burner has to work harder — wasting energy and creating hot spots that can crack the glass lining and the tank.
• On an electric heater, sediment can bury the lower heating element, causing it to overheat and burn out.
• It reduces the hot water you actually get and causes popping or rumbling sounds as water bubbles up through it.

Clearing it out keeps the heater efficient and helps it reach — or beat — its expected lifespan. (Wasted energy here shows up on your bill; the electricity cost calculator shows what your water heating costs to run.)

How often to flush

• Standard tank: about once a year.
• Hard water: every 6 months.
• Tankless: descale roughly once a year (a different process — circulating a descaling solution through the unit).

How to flush a tank water heater, step by step

You'll need a garden hose and maybe a flathead screwdriver. Plan for the tank to cool, so it's easiest to start a couple of hours after the last hot-water use.

1. Turn off the heat. Electric: switch off the breaker. Gas: turn the gas control to "pilot" or "off." Never drain a powered electric heater — the elements can burn out without water.
2. Shut the cold-water supply valve at the top of the tank.
3. Let it cool if the water is scalding hot — at least 30–60 minutes, or longer. This avoids burns.
4. Connect a garden hose to the drain valve at the bottom of the tank and run the other end to a floor drain, driveway, or outside (the water carries sediment, so not onto a lawn you care about).
5. Open a hot-water faucet somewhere in the house (and lift the tank's pressure-relief lever if you like) to let air in so the tank drains smoothly.
6. Open the drain valve and let the tank empty. Watch for cloudy, gritty water — that's the sediment leaving.
7. Flush it clean. With the drain still open, briefly open the cold-water supply to swirl fresh water through and push out remaining sediment. Repeat until the water runs clear.
8. Close the drain valve, remove the hose, and reopen the cold-water supply to refill the tank. Keep the hot-water faucet open until water (not air) flows steadily, then close it.
9. Restore the heat. Only after the tank is completely full — turn the breaker back on or relight the gas per the label. Powering an empty or partially filled electric tank ruins the elements.

When to call a plumber

Get a pro if the drain valve is stuck, leaking, or won't reseal, if the water stays rusty after flushing (a sign of internal corrosion), or if you'd rather not handle the gas pilot. Persistent rust, leaks around the base, or a heater past its expected age may mean it's time to replace rather than maintain — see how long a water heater lasts and estimate a swap with the water heater replacement cost calculator.

The bottom line

A yearly flush is cheap insurance: 30–45 minutes with a hose clears the sediment that quietly wastes energy and kills tanks early. Shut off the power or gas, let it cool, drain, rinse until clear, refill completely, then restore the heat — and your water heater will run more efficiently and last longer.