A sulfurous or rotten egg-like odor in the hot water is caused by bacteria growing in the water heater. This growth usually happens when the water heater is turned off while on vacation, when the hot water has not been used for a long time, or when the temperature setting on the heater is set too low. While the bacteria in the water heater are not a health threat, they must be eliminated to remove the odor problem.
Heat disinfection is used to eliminate the bacteria. It involves draining the water heater, maximizing the temperature in the water heater, and then draining the water heater again.
If you do not feel comfortable doing this work yourself, hire a licensed plumber to do it for you.
1. Select a time to drain the water heater. We recommend an evening since this will minimize the impact your typical use of hot water.
2. Turn the thermostat on the heater off so that only the pilot light remains on. If the heater is drained while the heating flame is on, the heater may be damaged.
3. Turn off the water supply to the water heater. There may be a valve to do this right at the inlet to the water heater, or the water supply to the entire property may need to be shut off at the house valve.
4. Open one or more hot water faucets inside the house. This allows air to enter the heater as the water drains out in step 6.
5. Attach a garden hose to the draincock located at the bottom of the water heater. The draincock usually looks like a regular hose bib (garden faucet) or a round dial with a threaded hole in the middle.
6. Extend the garden hose to a place where the water can be disposed of (e.g. a drain, the driveway, etc.).
7. Open the draincock and allow all of the water to drain out of the water heater. This can take anywhere from five minutes to half an hour or more depending on the capacity of the heater and the size of the draincock. Caution: the draining water will be very hot. Also note that if the draincock is made of plastic and the water heater is several years old, it may be difficult to open and may break easily if forced.
8. When the water heater is empty, close the draincock and remove the garden hose.
9. 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 them off.
10. That night (before going to bed), turn the thermostat for the water heater to its highest temperature setting for one night. Caution: make sure everyone who uses the water is aware that the hot water is going to be hotter than usual.
11. The next morning, turn the thermostat on the heater off so that only the pilot light remains on. If the heater is drained while the heating flame is on, the heater may be damaged.
12. Drain and refill the water heater by repeating steps 2 through 8.
13. Return the thermostat on the water heater to the normal setting (usually around 130°F).