How to Flush a Water Heater

The water coming into your home contains minerals. Over time, these minerals will begin to build up inside the water heater, where they settle on the bottom of the tank.

This sediment builds up over time. It can shorten the usable lifespan of a water heater and cause it to use more power.

How do you know if a water heater is full of sediment?

• The amount of hot water has reduced slowly over time.
• Tap on the tank, it should sound hollow. If it sounds different as you get closer to the valve, it's probably holding sediment.
• When the drain valve is opened and nothing comes out, it may be clogged with sediment.

Check the operator’s manual to find how often the manufacturer recommends draining or flushing it. Also, read the maintenance section to learn specific information regarding your water heater’s features and requirements. How to flush sediment out of a water heater varies slightly from one model to the next, but most steps are similar.

• Unless your operator’s manual suggests a different frequency, the water heater should be drained and flushed once a year.
• This yearly flushing is a good time to test the pressure relief valve and make sure the overflow drain is clear.
• Open the pressure relief valve for a few seconds to ensure that it’s working properly and that it allows some water to escape.
• Check the overflow drain to be sure that the water from the pressure relief test goes through.

• The operator’s manual also has valuable information about how to turn off the electrical power or gas for your specific water heater.
• If the gas burner or electric heating elements come on during the flushing process, the water heater can be damaged, requiring repair or replacement.
• Some manufacturers will recommend turning the gas off completely during this process, others may recommend setting the gas valve to the “pilot” or “vacation” setting.
• If you aren’t comfortable operating the gas valve or lighting the pilot light, contact a plumber about how to flush the water heater.
• Some gas utilities offer assistance with pilot lights on appliances like gas water heaters. Check with your provider to see if assistance is provided.
• Some electric water heaters will need to be turned off at the breaker. Others may have a plug like the one on an electric range, or have the ability to be turned off through a control panel or smartphone app.

In most cases, you will need to gather just a few items to flush a water heater.

• Garden hose, long enough to reach outdoors or a drain (if the drain is close enough, a washing machine supply hose will also work).
• Flat head screwdriver.
• Towel to dry spills.
• A bucket (optional).

• Water heaters often hold 40, 50 or more gallons of water.
• Some houses will have a floor drain near the water heater.
• If there’s no drain, the water can go outside, onto the ground.
• The discharge location needs to be lower than the drain valve on the water heater.
• If the water is hot, take the same precautions you would with hot water coming directly from a faucet.

• Turn off the electricity or gas, according to the manufacturer’s recommendations.
• Turn off the water on the inlet, or cold, side of the water heater.
• If there is no valve on the inlet, the water to the whole house will need to be turned off.
• Turn on a hot water faucet in the house. This is to admit air into the system and allow the water heater to drain.
• Attach the water hose to the drain valve. The valve will be located on the front of the water heater, close to the bottom.
• Route the hose to the drain or outdoors.
• The water will be hot, instantly. Take the same precautions with this water as would be taken with opening the hot water valve on a faucet.
• Open the drain valve on the water heater. It may have a handle or it may require use of a flathead screwdriver.
• The water will begin to drain from the tank. The time it takes depends on the volume of water the tank holds and if there are any clogs due to sediment.
• After the tank drains, slowly open the cold water inlet and allow it to run for a few minutes, or until the water from the hose runs clear.
• Close the drain valve and disconnect the hose.
• Allow the tank to refill.
• As the tank refills, air will sputter from the hot water faucet that is open inside the house. When the air stops and a stream of water comes from the faucet, turn the faucet off.

• If the gas was turned off, the pilot light will need to be lit when the gas is turned on.
• Turn on the electric power or gas to the water heater.
• Light the pilot light if gas was turned off or return the temperature to its normal setting.
• Check the area for signs of leaks.

• Tankless water heaters do not gather sediment like a water heater with a tank.
• Tankless water heaters can be flushed and cleaned but the process is more involved and requires special flush valves that are not standard on every system.
• The process uses chemicals and a circulation pump.
• If you have a tankless water heater, check with the manufacturer about required maintenance, including how to flush a tankless water heater.