Flushing and Disinfecting Water Heaters

How Do I Flush a Water Heater?

Over time, your water heater can accumulate sediment consisting of sand, gravel, and various mineral deposits. This buildup can reduce the amount your water heater holds, create a variety of interesting noises, and reduce the efficiency and life of your unit. Flushing your water heater can help resolve these problems. Also, the water heater will need to be flushed if the hot water becomes a yellow or brownish color due to an accumulation of rust, or if you find sand-like mineral sediment in the hot water. Follow the steps below to flush out your water heater.

• Turn off the heater! If your unit is gas, set the gas valve to "Pilot" to prevent the burners from coming on while you are flushing it. If your heater is electric be sure to turn off the circuit breakers. If the water level drops below the heating elements and the thermostat turns the elements on, the heating elements can burn out quickly. 
• Connect a garden hose to the drain valve at the bottom of the tank. The drain valve usually looks like a regular hose bib (garden faucet) or a round dial with a threaded hole in the middle. If the drain valve is made of plastic and the heater is several years old, it may be difficult to open and could easily break if forced.
• Make sure the outlet of the hose is in a safe area away from pets and children. 
• Close the shut-off valve on the cold inlet to the unit. 
• Carefully open the temperature/pressure relief valve at the top of the tank by lifting the lever. Leave the valve open. 
• Open the drain valve at the bottom of the heater allowing the water to flow out through the garden hose. 
• When the garden hose runs clear you are finished. 
• Close the drain valve at the bottom of the tank and remove the garden hose. 
• Close the pressure relief valve at the top of the tank and turn the cold inlet valve back on. 
• Open a hot faucet in your house, and let it run until no air bubbles come out. 
• Turn the heater back on.

If you do not feel comfortable doing this work yourself, hire a licensed plumber to do it for you. 

How Do I Disinfect a Water Heater?

A sulfur or rotten egg-like smell in hot water is caused by bacteria growing in the water heater. This usually happens when the water heater is turned off, has not been used for a long time, or when the temperature setting on the heater is set too low. The bacteria in the water heater are not a health threat, but they must be eliminated to stop the odor problem.

The procedure for eliminating the bacteria is called heat disinfection. It is a complex procedure that involves draining the water heater, maximizing the temperature in the water heater, and then draining the water heater again. This procedure is best started before bedtime or when the hot water is not needed for 8-10 hours. The steps are outlined below:

1. Turn the thermostat off so that only the pilot light remains on for a gas heater, or turn off the circuit breaker to an electric heater. If a heater is drained while the heating flame is on, or the power is still on, the heater may be damaged.
2. Turn off the water supply to the water heater. There should be a valve to do this at the inlet to the water heater, if not, the water supply to the entire property will need to be shut off.
3. Open one or more hot water faucets inside the house. This allows air to enter the heater as the water drains out.
4. Attach a garden hose to the drain valve located at the bottom of the water heater. The drain valve usually looks like a regular hose bib (garden faucet) or a round dial with a threaded hole in the middle. If the drain valve is made of plastic and the water heater is several years old, it may be difficult to open and may break easily if forced.
5. Extend the garden hose to a place where the hot water can be disposed of safely away from children and pets.
6. Open the drain valve and allow all of the water to drain out of the water heater. This process can take up to 30 minutes or more depending on the capacity of the heater and the size of the drain valve.
7. When the water heater is empty, close the drain valve and remove the garden hose.
8. Turn the water supply to the water heater back on. Leave the hot water faucet(s) inside the house turned on. This will allow the air in the water heater to escape as it refills with water. There will likely be "hissing" sounds and/or "spitting and sputtering" as air and water begin coming out of the hot water faucets. When the water flow from the faucet(s) returns to normal, shut it off.
9. Turn the thermostat for the water heater to its highest temperature setting for about 8 hours. Caution: make sure everyone who uses the water is aware that the hot water is going to be hotter than usual.
10. After 8 hours turn the heater thermostat off. Remember to turn off the heating flame or power before draining the unit.
11. Drain and refill the water heater by repeating steps 2 through 8.
12. Return the thermostat on the water heater to the normal setting (usually around 130oF).

If you do not feel comfortable doing this work yourself, hire a licensed plumber.