Water heater maintenance: how to flush the tank, test the relief valve and check the anode rod

Your water heater works hardest in winter, when incoming water is coldest and everyone wants a longer shower. It’s also easy to forget until it fails, usually with a puddle on the basement floor. A little yearly upkeep helps it last longer and run more efficiently. The U.S. Department of Energy says periodic maintenance can significantly extend a water heater’s life and limit lost efficiency over time.

This guide covers a standard tank water heater (gas or electric). Your owner’s manual comes first: model-specific steps and intervals vary, and the label on the tank lists the manufacturer’s instructions. If you’re not comfortable working around gas or electricity, hire a pro for the whole job.

How often to do each task

• Temperature setting: check once a year, and any time the water seems too hot or not hot enough.
• Temperature and pressure (T&P) relief valve: A. O. Smith says homeowners should check it once a year and have a professional inspect it every 5 years. An older DOE fact sheet suggests checking it every six months.
• Flushing sediment: most tank models need a flush at least once a year, and more often if you have hard water (A. O. Smith). DOE’s older guidance is to drain about a quart from the tank every three months.
• Anode rod: A. O. Smith recommends inspecting it once a year. DOE’s older fact sheet says every three to four years. Hard water, a water softener and heavy use all wear it out faster.
• Gas models: have the burner, combustion chamber and flue checked once a year, and keep a carbon monoxide alarm nearby (DOE).

Before you start

• Turn off the heat source: switch off the breaker for an electric heater, or turn the gas control to “off” (or “pilot”, per the label) on a gas model.
• Let the water cool for a few hours if you can. Tank water is hot enough to scald, so wear thick gloves and safety glasses.
• Find the cold-water shutoff valve on the pipe above the heater, and know where your home’s main shutoff is in case something leaks.
• Have a garden hose, a bucket and some old towels ready. Some drain valves need a flathead screwdriver to open.

Step 1: Set the temperature to about 120°F

The U.S. Consumer Product Safety Commission recommends setting water heaters to 120°F to reduce the risk of tap-water scalds, which are most dangerous for young children and older adults. DOE notes that 120°F meets most household needs and lowering the setting saves energy. Don’t go much lower: A. O. Smith warns that too low a setting can let bacteria grow.

On a gas heater, the dial is on the gas control at the bottom. On an electric heater, the thermostats sit behind access panels, so turn the power off first. After a few hours, check the temperature at the faucet nearest the heater with a kitchen thermometer.

Step 2: Test the T&P relief valve

The T&P valve is a safety device that opens if the tank gets too hot or the pressure gets too high. A. O. Smith warns that if it doesn’t work, the tank can over-pressurize and explode, so this test matters.

Put a bucket under the discharge pipe, then lift the valve’s lever to open and close it a few times. Water should rush out and stop when you let go. If nothing comes out, or it keeps dripping after you release the lever, call a plumber to replace the valve. A valve that drips on its own usually means water pressure is too high or the home needs a thermal expansion tank, which a plumber should check before simply swapping the valve.

Step 3: Flush the sediment

Minerals in your water settle at the bottom of the tank. Over time that sediment can reduce efficiency, cause rumbling or popping noises, and clog the drain valve.

Turn off the heat source and close the cold-water supply. Attach a hose to the drain valve at the bottom of the tank and run it to a floor drain, outside, or a bucket. Open a hot-water faucet in the house so air can enter, then open the drain valve. To flush, briefly turn the cold supply back on and let water run through until it comes out clear. Close the drain valve and remove the hose. With the cold supply open, leave a hot faucet running until water flows steadily with no sputtering air. Only then turn the power or gas back on.

Important for electric heaters: the tank must be completely full before you restore power, or the heating element can burn out (A. O. Smith). If the drain valve is clogged with sediment and won’t flow, stop and call a plumber rather than forcing it.

Step 4: Check the anode rod

Steel tanks have a sacrificial anode rod, usually magnesium, aluminum or zinc, that corrodes so the tank doesn’t. Once it’s used up, the tank itself starts to rust from the inside, which is how many heaters fail early.

Checking it means draining a few gallons, then unscrewing the rod from the top of the tank (A. O. Smith uses a 1-1/16-inch socket). A healthy rod is about half an inch thick. If it is badly worn or shows several inches of bare core wire, replace it with the type your model calls for. Rods can be stuck tight and hard to reach under low ceilings, so many owners have a plumber do this part during a service visit.

Step 5: Look for problems while you’re there

• Leaks or rust at the pipe connections, the drain valve or the bottom of the tank. Water pooling under the tank itself (not from a fitting) usually means the tank is failing.
• On gas models: a vent pipe that’s loose, rusted or not sloped up to the chimney or flue, and soot or scorch marks near the burner. Have those checked right away and make sure there’s a working CO alarm nearby.
• Clutter: keep paint, gasoline and other flammables away from a gas heater, and don’t block the air openings.
• Pipes in unheated spaces: insulating hot and cold lines near the tank cuts heat loss and helps prevent freezing. DOE suggests insulating at least the first six feet from the tank.

When to call a plumber

Call a licensed plumber if water is pooling under the tank, the T&P valve won’t open or keeps dripping, you smell gas, the drain valve is clogged, you see rust-colored hot water or the tank is making loud banging noises. Call one too if the heater is old and you want an honest opinion on repair versus replacement. Many states and cities require a permit and a licensed installer to replace a water heater, so ask who pulls the permit when you compare quotes. In cold-climate homes, a winter breakdown is a good reason to plan ahead instead of replacing in a rush.

Put it on the calendar

Pick a date each year, such as the day the clocks change in the fall, and do the five steps above. A free Estodia account puts the water heater flush and anode check on each home’s maintenance plan, reminds you when it’s due, and lets you request quotes from local plumbers without sharing your phone number or email with them. No spam.

• How to prevent frozen pipes
• Before you light the first fire: chimney and carbon monoxide checklist
• A home maintenance calendar, season by season
• The full home maintenance checklist
• How to compare contractor quotes

Related guides

• Furnace tune-up checklist
• Dryer vent cleaning: how often and how to check
• Test your home for radon this winter