How To Clean and Flush a Water Heater

The way a water heater works, cold water enters through a dip tube that runs down to the bottom of the tank and hot water exits from the top of the tank. This results in sediment, rust, and contaminants from the water sinking to the bottom of the tank where it builds up over time.

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Allowing the sediments and calcium deposits to build up in the tank may result in loss of heating power, failed components such as clogged pipes or the heating element, and possible health issues for those who use the water. To get the safest and most dependable use from your water heater, cleaning it annually is the best way to go. Here’s how to flush a water heater…

Drain the Water Heater

Connect a garden hose to the hose bib near the bottom of the water heater and extend the hose to a floor drain or outside location.

Note: If you have a drain pan underneath that is correctly plumbed to a drain, no hose is necessary.


Turn off the power to the water heater or set the gas control valve to the “Vacation” setting. Close the cold water inlet valve which is usually located at the top of the tank. Open the drain valve and turn on the closest hot water faucet to allow air into the tank.

See Also:  6 Ways to Unclog a Water Heater That Won’t Drain

Allow the tank to empty fully before proceeding. Obviously, larger hot water heater sizes will take a bit longer to drain but it shouldn’t take more than a few minutes.

Remove the garden hose from the drain valve. If your water heater has a plastic drain valve, this is a good time to replace it with a more durable brass valve. Using a large adjustable wrench, remove the drain valve and replace with the brass valve.

Cleaning and Flushing the Tank

Your local hardware store will sell a long, narrow brush (like this) that is designed for refrigerator coils but is also excellent for water heater tank cleaning.

Insert the brush into the opening where the drain valve was removed. Carefully use the brush to scrape the bottom of the tank and as much of the interior sides of the tank as you can reach.

If your tank has not been cleaned in a while, this can take a bit of time. The more of the sediments you can break loose, the better your water heater will function.

Screw a short 3/4 inch plumbing nipple into the drain opening. Drain valves are not suitable for tank cleaning because they are easily clogged by the debris that will be flushed out.

Place a bucket directly below the plumbing nipple or connect a garden hose to the other end of the nipple (or let it drain into a properly installed drain pan). Insert the other end of the hose (if using one) into a bucket so you will be able to see the results of your cleaning.

Turn on the cold water inlet valve and allow it to run until the water coming out of the hose clear. Remove the nipple and repeat the process until no more sediments are washed out after scrubbing. There may be rust, calcium deposits or other debris in the bucket.

Note:  Many newer water heaters include “self-cleaning” feature. While helpful, you still want to manually flush and clean a water heater but you simply don’t have to do so as often. So instead of an annual cleaning, doing so every 3 years or so should suffice.

Completing the Project

Turn off the hot water faucet. Instead of replacing the drain valve, you can install an inline ball valve on the end of the nipple to make future cleaning easier. You will need to add a second, short nipple to the outlet side of the valve.

Wrap the threads on both ends of the nipple with plumber’s tape and tighten the nipple securely into the tank. Screw on the ball valve and tighten it properly.

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Turn on the cold water inlet valve. Turn on the hot water faucet and allow it to flow until all air has escaped the line. When the air has been removed from the tank, restore power or set the gas control valve to the “On” position.

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  1. I wouldn’t stick anything up there — draining your water heater once a year is quite sufficient. Water should not come out that nasty looking if you do it yearly even with hard water. Mine comes out somewhat cloudy only then clear.

    • True… IF you’re diligent about an annual cleaning. I would bet most homeowners have never drained a water heater tank but it’s a great (and easy) preventive measure.

  2. I had no idea you were supposed to clean out a water heater every year. I came here because my water heater had a slow leak for some time. Our water heater is as old as our house (almost 10 years). Do you think the inside of tank is now all messed up because we’ve never cleaned/flushed it?

    • I think you have already *REPLACED* your water heater… Leaks seldom if ever ‘fix’ themselves, and are fairly awkward and messy to consciously *fix*, so are usually rectified by replacing the unit…

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