Q: I have a hot water heater that is about 12 years old. It was top of the line when I bought it. About a year ago, it started making big boiling-bubble sounds when we used the hot water. It’s directly under our dining room, so the noise is very noticeable.

Also, my mom has a water heater that is brand-new and makes those same big popping noises. What causes this? Can it be repaired? Is it time to get a new heater, and if so what kind do you recommend? Is my mom’s new heater defective?

A: “Bubble, bubble, toil and trouble.” A gurgling water heater directly below your dining room table is annoying and cause for some alarm. Fear not, though. We doubt that the water heater is about to explode.

To answer two of your questions: Your water heater is toward the end of its useful life, but it may not need replacing just yet. Your mom’s water heater probably is not defective, but it sounds as if it could use some maintenance.

As to the cause of the noise, a noisy water system can be diagnosed by the sound it makes. Water hammer, for example, is pounding and vibration created when water flowing through a pipeline is stopped abruptly. This occurs when a faucet is abruptly closed or the solenoid valve in a dishwasher or washing machine closes.

Water hammer can be cured by installing arrestors in the water line. These dampen the shock waves causing the noise.

Although you report that the noise coming from your water heater and your mom’s is the same, the cause may be different.

Your heater is 12 years old, and it just started gurgling about a year ago. This indicates something’s changed. Attached to a service manual from A.O. Smith Water Products Co., a nationally known manufacturer of gas and electric water heaters, is a series of technical bulletins concerning noisy water heaters. These bulletins may be accessed on the Internet at www.hotwater.com/bulletin/main1.htm.

The boiling, bubbling sounds you describe are most likely the result of mineral buildup in the tank. A.O. Smith’s Technical Bulletin 13, titled “Mineral Build-up,” gives a detailed discussion about the symptoms, cause and cure for a “rumbling,” “crackling” or “popping” water heater.

Lime (CaCO3) is the most common element in “hard” water. It is present to some degree in virtually every water system in the United States.

Lime is inversely soluble. That is, 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.

Symptoms of lime buildup include popping of water escaping from under lime deposits or sizzling water trapped next to heating elements being boiled to steam.

Treatment of a limed-up tank is relatively simple and can be tackled yourself. Lime is a base, and the easiest way to neutralize it and dissolve it so that it may be flushed from the water heater is with an acid.

The most commonly used de-liming acid is phosphoric acid at a food-grade level. A well-stocked plumbing supply house should have a de-liming solution. Follow manufacturers’ instructions carefully when using these products.

Your mom’s newer water heater also might be suffering from mineral buildup. But there could be another cause.

In parts of the United States where the water supply has a high pH, it might react with the aluminum anode in newer water heaters and produce excessive amounts of aluminum hydroxide. This by-product settles to the bottom of the tank near the heating element and interferes with combustion.

Check for this condition by removing an aerator from a faucet. Blue, green or gray jellylike beads in the aerator are indicative of aluminum hydroxide. Excessive aluminum hydroxide buildup can be cured by replacing the aluminum anode with a magnesium anode. Unless you are skilled in working with pipes, this job is probably better left to a plumber.

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