If pressure builds up in a 30-gallon water heater that has a non-operational temperature & pressure relief valve, an explosion can result that is equal in force to two pounds of dynamite. Experts say that one-third of all water-heater temperature- & pressure-relief valves are not operational -- due to mineral buildup, rust or corrosion. These valves should be tested every six-months or so by operating the test lever at the top of the relief valve. If the lever won't budge, tap it lightly with a small hammer. If a leak follows your test, operate the lever several more times to dislodge debris that may be holding the valve open. If you can't stop the leak -- replace the valve. Frequent checks will guarantee leakfree tests. And that's The On House tip for today.