Q: We recently purchased an older home and have no idea how old the water heater is. When the water is heating up, we hear a loud bubbling sound as if the water is boiling. Is this normal?

In addition, it recently started giving off an odor resembling rotten eggs. We thought the pilot light was out, but it wasn’t. We even called the fire department to check and they said it was fine.

Do you think our water heater is broken or defective?

A: Your water heater isn’t broken or defective; it’s probably just old and maybe worn out.

You should be able to determine the age of your water heater by locating a rating plate on the heater body. One of the pieces of information on the plate is the date the heater was manufactured. Be warned, the numbers on the plate will seem like the DaVinci code. For decoding help, visit www.fastwaterheater.com/model%20%20serial%20number.htm.

It’s a pretty safe assumption that the heater was placed into service within a year or two of the manufacture date. For example, Kevin’s water heater shows an October 1991 date of manufacture. He placed it into service in mid-1994.

Water heaters are warranted for various life spans. Six-, nine- or 12-year warranties are most common. Usually the longer the warranty, the heftier the construction inside the heater. If your heater is older than the warranty, you’re living on borrowed time. But that doesn’t mean replacement must be done tomorrow. Kevin’s water heater came with a five-year warranty and is still going strong.

The bubbling sound you hear when the water heater fires up is most likely the result of mineral buildup in the bottom of the tank. It’s common in older water heaters. The rotten egg smell probably comes from bacteria growing in the water heater.

There are fixes for both of these problems, but unless you plan on doing it yourself, you might be money ahead by installing a new water heater.

A.O. Smith Water Products Co., a nationally known manufacturer of water heaters, publishes a series of technical bulletins. These bulletins may be found at www.hotwater.com/bulletin/main1.htm.

A.O. Smith’s Technical Bulletin 13, titled “Mineral Build-Up,” gives a detailed discussion about the symptoms, cause and cure for a “rumbling” water heater.

Lime is the most common element in “hard” water. It is present to some degree in virtually every water system in the United States. The more heat applied to the water, the more lime leaches out. High usage, hard water and time can lead to a limed-up water heater tank.

Treatment of a limed-up tank is relatively simple. Lime is a base, and the easiest way to deal with it is to neutralize it and dissolve it so that it may be flushed from the water heater. The most commonly used de-liming agent is phosphoric acid at a food-grade level. A well-stocked plumbing supply house should have a de-liming agent. Follow manufacturers’ instructions carefully when using these products.

The rotten egg smell is probably caused by the sulfate-producing bacteria in the water. While the smell is a nuisance, the bacteria are not harmful. A quick fix might be to turn up the temperature of the water heater past 140 degrees. According to A.O. Smith, the responsible bacteria thrive at temperatures below 138 degrees.

If this doesn’t work, the next simplest solution is to “shock-chlorinate.” This is a complex procedure and something you may not want to tackle given the probable age of your water heater. For a detailed explanation and an overview of the suggested treatment, go to A.O. Smith’s technical bulletin at www.hotwater.com/bulletin/bulletin23.pdf.


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