Weekend Project: Flush your water heater

Consumer Reports News: March 12, 2010 01:40 PM

Flushing a water heater can help it last longer.
Sediment in your water supply, in the form of hard-water minerals like calcium and other small particles, including rust and sand, can damage a gas or electric storage-tank water heater and shorten its life expectancy. And for an electric water heater, the cooler tank bottom that can result from this damage can become a breeding ground for legionella.

Most storage-tank water heaters are fairly reliable, but once a tank leaks, it's time to replace the water heater since a repair isn't generally worth the cost.

To keep your water heater from springing a leak and ensure that it's working efficiently, flush it a couple of times a year. The beginning and end of daylight-saving time—which for 2010 starts this Sunday, March 14—are good opportunities to tackle this basic chore. If your Consumer Confidence Report from your water company or a home water test reveals hard water, you might want to flush your heater more often.

Here's how to flush your electric or gas water heater, as adapted from our Complete Guide to Reducing Energy Costs ($19.45, including shipping). We also suggest that you check the manufacturer's instructions.

Before you start this project, turn off the water heater. (Running the appliance while flushing it wastes energy and can also damage the appliance or present a safety hazard.) If you have an electric water heater or a gas unit with electronic ignition, turn off the heater at the breaker panel, fuse box, or cutoff box (shown above). If you have a gas unit with a gas pilot, turn the gas valve to "pilot."

1. Shut off the cold water. Turn the cutoff valve in the line that supplies cold water to the water heater. Initially, you want the tank to drain without refilling.

2. Open a hot-water tap anywhere in your home. This will allow air to displace the water in the tank and tank drain more quickly and thoroughly.

How to flush water heater sediment

3. Open the draincock. Put a hose on the draincock at the bottom of the tank and run it to the drain; the drain must be below the tank so it can work by gravity. Open the drain valve/spigot and let the tank drain. The draining water will probably be cloudy at first.

Let the water continue to drain for a few minutes after it has turned clear and then shut the drain valve/spigot. Wait a few minutes and reopen the drain valve/spigot to see whether the water remains clear. If it does, go to the next step. If it doesn't, repeat this process until the water is clear. Be careful: The water will be extremely hot and could scald you.

4. Refill the tank.
When you are finished flushing the tank, close the drain valve/spigot. Open the valve on the cold-water supply line and add water to the tank for a few minutes, then shut the cold water and open the drain valve/spigot. Let the water rinse the tank. If the water runs clear, close the drain valve/spigot and the hot-water tap and open the cold-water supply to fill the tank. Then turn the water heater back on. It the water runs cloudy, repeat the process from step 3.

If you don't have a drain point below the level of the tank, you can drain the tank using the water pressure from the cold-water supply—simply leave the cold water on and do not open any other faucet. Use a hose to route water from the drain valve/spigot to any drainage point. But before you use this method, allow the tank to cool so that any hot water that leaks from a drain hose won't present a scald hazard. Note that because the cold water entering the tank will stir up the debris from its bottom, flushing the tank might not be as thorough.

How to flush water heater

Essential information:
If you need a new water heater, see whether your state is offering an incentive as part of the $300 million cash for clunkers for appliances rebate program. Read our reviews of solar water heaters, tankless water heaters, and the new GE GeoSpring electric heat-pump water heater. Performance comparisons of storage tank and tankless water heaters are available to subscribers. Finally, join in the discussion in our water-heater forums.

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