Doing talk-radio is interesting. Callers ask their questions in a minute or less and we must answer equally briefly.

As with this column, we do a lot of research to ensure that the information we provide is not only correct, but timely, as well.

A recent caller had a question about a water heater. As an adjunct to our answer, we suggested that she toggle the lever on the temperature-and-pressure-relief valve (T & PR valve) every six months or so to be sure that it was operating freely. The T & PR valve opens to release pressure buildup from within the water heater, thus preventing a possible explosion. She thanked us and the program continued.

About twenty minutes later our computer monitor showed that a caller was on the line who wanted to scold us for advising our listeners to test T & PR valves. When he came on the line he stated that he worked for a water heater company and that it was their recommendation to never test a T & PR valve, and that we should not have recommended such a procedure. This was because, according to the caller, "testing could cause the valve to leak and would most certainly damage the spring within the valve."

We felt we were correct, but neither of us could recall the source of our recommendation. We thanked the caller for his comments, advising him that we would research the matter further.

We then contacted the folks at Watts Regulator Company in North Andover, Mass., a firm that manufactures T & PR valves. We spoke to one of their technical service representatives who advised us that the company recommends an annual check of their T & PR valves. The reason: mineral salt, rust and-or corrosion build-up can cause a T & PR valve to freeze up and become non-operational, which, she said, can lead to a water heater explosion. She offered an interesting parallel that we thought might interest you. When a water heater explodes the force generated is equal to that caused by a stick of dynamite (other sources say two pounds of dynamite for a thirty gallon unit).

So, if you want your water heater to be as safe as it can be, make sure that the T & PR valve is operating freely. If the valve wasn't supposed to be tested, it wouldn't have a lever designed specifically for that purpose, and appropriately named by the manufacturer, the "test lever."

Larry & Suzanne Weingarten, authors of the "Water Heater Workbook," authorities on water heaters and accessories, tell us that they recommend testing every six months. More frequent testing can reduce the chance of a leak caused by mineral and corrosion build-up. However, Larry tells us that if a leak results immediately after a test, to simply operate the test lever several times in an attempt to free lodged debris that may be preventing tight reclosure of the valve.

Testing ensures that the valve is operational. If you don't think testing is important at your home, check out this statistic: According to a survey done by Domestic Engineering Magazine, approximately one of every three T & PR vales is frozen shut and non-operational.

The Weingartens also tell us that the pipe leaving the relief valve should be the same diameter as the exhaust port of the valve (usually three-quarters of an inch). Also, the pipe should be made of a material that is not affected by heat. Copper is a safe choice.

The T & PR drain pipe should travel in a slightly downhill direction from the valve to the point where it terminates. And, it should end outside the house at six to 24 inches above the ground. If the drain pipe moved uphill first and then downhill, water could get trapped against the outlet of the valve and corrode it shut. If the drain line had a trap or a low spot, water could freeze. And even if the valve was working, pressure would be captured and an explosion might occur.

As consumers, we spend much of our time worrying about when our water heater is going to begin leaking and therefore need replacement. If one maintains a water heater properly, it will last a very long time. Also, it will operate more safely and cost effectively. If you want to know more about your water heater and its operation we suggest you pick up a copy of the "Water Heater Workbook" by Larry and Suzanne Weingarten. Send a check for $12 to Elemental Enterprises, P.O. Box 928, Monterey, CA 93942.