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How to Back-Flush a Water Heater

Back-flushing a water heater is required when mineral deposits in the tank prevent the water heater’s drain valve from allowing you to flush or empty the tank. For information flushing the tank, please see How to Flush or Drain a Water Heater. In that article, you’ll see that a first step in breaking up a drain clog can be simply stepping on the hose as water is draining to pump water back into the tank.

Hose Coupler    Photo: Bosch

Double-Female Hose Coupler Photo: Bosch

If pumping the drain hose with your foot doesn’t do the job, you’ll need to move on to a more aggressive approach: back-flushing the water heater.

To back-flush a water heater, you’ll need a garden hose and a double-female garden hose coupler (available online for about $8).

1First follow the preparation discussed in the article How to Flush or Drain a Water Heater.

2Turn off the water heater’s drain valve by turning it clockwise.


3Using the female hose coupler, attach the male end of the garden hose to an outdoor hose bibb (faucet) or washtub faucet.

4Turn on the faucet to charge the hose with water pressure.

5Open the water heater’s drain valve. Water should rush into the water heater, pushing deposits away from the valve.

6Turn the water heater’s drain valve off again, and then turn off the water faucet.


7Unscrew the hose from the water faucet, and try flushing the tank again. If it still doesn’t drain well, the next step is either to replace the water heater’s drain valve or to replace the water heater.

Water Heater Drain Valve

Water Heater Drain Valve

First Steps in Breaking a Drain Valve Clog

Depending upon whether the water heater is gas or electric, turn off the gas valve or circuit breaker that powers it. Connect a hose to the drain valve and run it outside, placing the end of the hose below the level of the water heater. Turn on a hot water faucet somewhere in the house or open the water heater’s pressure-relief valve to break the vacuum inside the tank. Then open the drain valve. If the water runs freely, the valve works. If it doesn’t, it’s probably clogged.

If you suspect that the drain valve is clogged, you can try repeatedly stepping on the hose a couple of feet away from the tank to squirt water and air bubbles back into the tank. Hopefully this will break loose the clog. If it doesn’t, back-flush the water heater as described above.

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About Don Vandervort
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Don Vandervort developed his expertise more than 30 years ago as Building Editor for both Sunset Books and Home Magazine. He has written more than 30 home improvement books and countless magazine articles. He appeared regularly on HGTV’s “The Fix,” and served as MSN’s home expert. Don founded HomeTips in 1996.

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