How to Flush or Drain a Water Heater Safely

Step by step

1. Turn off the heat. For gas, turn the control knob to OFF or PILOT as the label directs. For electric, switch off the water heater's breaker.
2. Let the water cool if you can. The CPSC says 140°F water causes third-degree burns in 6 seconds, and tank water is often that hot.
3. Close the cold-water supply valve on the pipe that feeds the top of the tank.
4. Connect a garden hose to the drain valve near the bottom of the tank and run it to a floor drain or outdoors, where hot water cannot hurt people, pets or plants.
5. Open a hot-water faucet somewhere in the house so air can enter and the tank can drain.
6. Open the drain valve. Let it run until the water comes out clear. To stir up sediment, briefly open the cold supply with the drain still open, then close it again.
7. Close the drain valve, remove the hose and open the cold-water supply to refill the tank.
8. Leave the hot faucet open until water flows steadily without sputtering. That means the tank is full.
9. Restore heat: relight or turn the gas control back on following the label, or switch an electric heater's breaker on only after the tank is full.
10. Check the drain valve for drips over the next day. A valve that will not stop dripping needs replacement.

How often should you flush a water heater?

DOE's Energy Saver guide recommends draining a quart of water from the tank every 3 months to remove sediment, which impedes heat transfer and lowers efficiency, and says to follow the manufacturer's directions. Homes on harder water benefit from a full flush more often.

Tankless units need descaling rather than draining. A DOE Building America guide says manufacturers recommend it anywhere from twice a year to once every three years, depending on the model, how much hot water you use and your water quality.

What is the difference between flushing and draining a water heater?

Draining empties the tank, which you do before a replacement or some repairs. Flushing is draining plus running fresh water through the tank to stir up and rinse out sediment. Both use the drain valve, and both require the heat to be off first. Never switch an electric heater back on until the tank is full again, or the elements can burn out.

How do you flush a tankless water heater?

Turn off power and gas to the unit and close its water service valves. Connect hoses and a small pump to the service ports, circulate the descaling solution your manufacturer specifies for the time the manual gives, then flush with clean water and clean the inlet filter if there is one. If your unit has no service valves, a plumber can install them; HomeGuide puts professional tankless maintenance at $75 to $300 nationally.

Does Sacramento-area water cause more sediment?

It depends on your supplier. The U.S. Geological Survey classifies water with 0 to 60 mg/L of hardness as soft, 61 to 120 as moderately hard, 121 to 180 as hard and more than 180 as very hard. Local 2025 water quality reports show a wide range.

• Soft surface water: El Dorado Irrigation District averages 13 mg/L, San Juan Water District 17, PCWA's Foothill/Sunset system about 22, Folsom 26.5 and Roseville's Folsom Lake water 26.
• Moderately hard on average: City of Sacramento 83, Davis 72 (weighted) and Woodland 69.4. West Sacramento averages a soft 47 but ranges up to 180.
• Hard to very hard well water in some systems: Elk Grove Water District Service Area 1 averages 141 (62 to 240), and Sacramento Suburban Water District's South Service Area wells range from 51 to 280.
• Check your own supplier's Consumer Confidence Report; the tankless water heater page on this site has a table for 19 local systems.

When should you call a plumber instead of flushing it yourself?

Call a plumber if the drain valve will not open or will not stop dripping; Fixr notes drain valves can wear out and start leaking right after a drain, and replacement runs $100 to $200 nationally. Call if the flow stops early because sediment has clogged the valve, if the relief valve drips after refilling, or if you smell gas at any point; in that case leave and call 911, then PG&E. A plumber can also check the anode rod while the tank is drained; HomeGuide says plumbers recommend replacing it every 3 to 5 years.

Frequently asked questions

Available across the Sacramento area

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