Q: I read with interest your articles on water hammer, and have a question. I have an older gas water heater. It works fine, heats well and has no leaks, but as of late, makes the most horrible grinding and gurgling noises as it fills and heats after hot water use. It sounds something like the boilers of a ship sinking at sea. Any clues?

A: Oh yeah. We’ve got more than a clue — we’re confident we know the problem. Better yet, we may have a fix.

The horrible noise you hear when the water heater fires up is probably caused by mineral buildup in the bottom of the tank. Hot water rises and flows by convection to the top of the tank. When you take a shower or turn on the dishwasher, the hot water you use is replaced by cold water that migrates to the bottom of the tank to be heated.

The thermostat sends a signal to turn on the burner. After the flame goes on at the bottom of the tank, the water heats up. Normally there is no noise. But, when there is too much sediment on the bottom of the tank the heated water makes its escape with anything from a "wheeze" to a "gurgle" to a resounding "pop." It may sound like the sinking of the Titanic, but not to worry, it can be fixed.

So, you have an "older" heater. How old is old? If it’s real old and you haven’t done regular maintenance on it, you may just want to bite the bullet and replace it. After all, it could die any day.

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 significantly 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 going strong after 13 years. He’s been lucky. He’s borrowed a lot of time.

As far as the fix, regular maintenance is the key. The best thing a homeowner can do is to flush the water heater on a monthly basis. This simple process involves hooking up a garden hose to the drain valve at the base of the heater, opening the valve and with the water inlet valve open to maintain the pressure in the tank, allowing the water to flow until the water runs clean. Try this first. It may help. If not, de-liming is the other option.

A.O. Smith Water Products Co., a national manufacturer of gas and electric water heaters, publishes a series of technical bulletins. Bulletin No. 13, titled "Mineral Build-Up," gives a detailed discussion about the symptoms, cause and cure for a "rumbling," "crackling" or "popping" water heater.

The cause of the bubbling is lime buildup. Lime 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. Treatment of a limed-up tank is relatively simple. Whether it’s a do-it-yourself project depends on the skill of the homeowner.

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 agent is food-grade-level phosphoric acid.

A well-stocked plumbing supply house should have a de-liming solution. If you’re going to tackle the job yourself, make sure you have the appropriate skill level to work safely with gas and water pipes and follow manufacturers’ instructions to the "T" when using these products.

If a search at the plumbing wholesaler proves fruitless, a product called Un-lime is available from A.O. Smith. If you’re thinking about doing your own de-liming, we suggest you download the technical manual from A.O. Smith, which provides a detailed description of the de-liming process and appropriate cautions.


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