How to flush your water heater, and when it's a plumber's job
Minerals in the water settle at the bottom of a tank water heater. This grit is called sediment1. A. O. Smith says most heaters should be flushed at least once a year2. Rheem says every 6 months if your water is hard, and that tankless heaters need a different cleaning, called descaling1. These steps are for tank heaters.
New Jersey's health department strongly recommends hiring a plumber for this job3. If you do it yourself, these steps follow its guide and the U.S. Department of Energy's. The signs that it's a plumber's job come from the makers.
Smell gas? Leave right away. Don't turn on lights or appliances, and don't use your phone. Call for help from a neighbor's phone.4
The yearly flush, step by step
Read your own heater's manual first; where it differs from these steps, follow the manual3.
- Turn the heat off: the breaker for an electric heater; for gas, off or “pilot”, as your manual says.5,2
- Let the water cool, typically overnight, or run the hot taps until the tank water is cold.3,6
- Close the valve on the cold-water pipe into the tank, and open a hot tap so air can get in.5
- Attach a hose to the drain valve. Run it to a floor drain or outside, lower than the bottom of the tank. Wear thick gloves and safety goggles.5,2
- Open the drain valve and let the tank empty. Then, with the drain still open, slowly open the cold-water valve again. Let it run until the water from the hose runs clear.5,3
- Close the cold-water valve. Then close the drain valve and check that it doesn't drip.3
- Open the cold-water valve again so the tank refills. Leave the hot tap open: it sputters while air comes out. Once it runs smoothly, the tank is full. Turn the tap off.3,5
- Only then turn the power or gas back on. For gas, follow your manual to relight the pilot or keep it lit.5,2
Who should not do this: Have a plumber do it if you are 50 or older or if you smoke. Do the same if you have a weak immune system, long-term lung disease or another health problem. The spray can carry germs.3
When it's a job for a pro
- The drain valve won't open or leaks.1,2
- There is heavy rust around the pipe joints, or the noise keeps going after flushing.1
- The heater is 8 years old or older.1
- You aren't sure how to handle the heater's gas or electrical parts.1
- CrewButton doesn't check licenses. Before you hire, check the plumber's license on the state board's license search.7
Why it matters
- The New Jersey Department of Health says sediment can help germs grow, including the germs that cause Legionnaires' disease.3
- The U.S. Consumer Product Safety Commission urges setting water heaters to 120 °F. Most adults suffer third-degree burns after 2 seconds in 150 °F water, or 6 seconds in 140 °F water.6
- A water heater that turns on while it is empty or partly empty can be damaged quickly. So don't turn the heat back on until the tank is full. If you skip the cool-down, the water coming out of the tank will be hot.5
Replacing instead of flushing
- In a Texas city of more than 5,000 people, replacing a water heater needs a plumbing permit. Water heaters are not on the state's short list of jobs that skip the permit.8