DEAR BARRY: We have a 50-gallon water heater in our basement. It’s only 7 years old, but it has always leaked from the drain pipe on the pressure relief valve. We’ve tried everything to stop the leak. We turned down the thermostat, flushed out the tank, and replaced the relief valve twice. But the problem always returns. Why doesn’t this leak stop after all we’ve done to fix it? –Mark

DEAR MARK: Before answering your question, a few words should be said in praise of "temperature pressure relief valves," commonly known as TPR valves. A water heater is not safe without a TPR valve. Its primary purpose is to prevent an explosion when a water heater becomes too hot. TPR valves have been mandatory for all water heating systems since the late 1960s. Before then, an overheated tank could become a bomb, causing massive property damage and possible injury or death to nearby occupants.

DEAR BARRY: We have a 50-gallon water heater in our basement. It’s only 7 years old, but it has always leaked from the drain pipe on the pressure relief valve. We’ve tried everything to stop the leak. We turned down the thermostat, flushed out the tank, and replaced the relief valve twice. But the problem always returns. Why doesn’t this leak stop after all we’ve done to fix it? –Mark

DEAR MARK: Before answering your question, a few words should be said in praise of "temperature pressure relief valves," commonly known as TPR valves. A water heater is not safe without a TPR valve. Its primary purpose is to prevent an explosion when a water heater becomes too hot.

TPR valves have been mandatory for all water-heating systems since the late 1960s. Before then, an overheated tank could become a bomb, causing massive property damage and possible injury or death to nearby occupants. With a TPR valve, steam and pressure are safely released from an overheated tank, preventing a potential explosion.

When a TPR valve leaks there are three possible causes: 1) excessive temperature; 2) excessive water pressure; or 3) corrosion or debris on the valve seat. Some TPR valves leak after being tested, usually because of corrosion on the valve seat. Thus far, you have addressed most, but not all, of these possible causes. You lowered the temperature by adjusting the thermostat; you eliminated corrosion and debris by flushing the tank; and you installed a succession of new relief valves. So let’s examine the remaining possibilities.

Turning down your thermostat was a wise move, but what if the thermostat is defective and did not actually cool down the water? This point needs to be verified. To test the water temperature, place an oven thermometer in a pot and submerge it in steaming water from the tap. The recommended temperature in a water heater is around 120 degrees.

If your water temperature is significantly higher, especially if it is approaching 200 degrees, you have a problem and should call a licensed plumber immediately. If the temperature is normal, then we have narrowed our search to high water pressure.

To check the water pressure, you’ll need a pressure gauge with a fitting for a hose faucet. This can be purchased at your local hardware store for about $12 to $20. Simply attach the gauge and turn on the hose faucet. The recommended pressure for a residential plumbing system is 50 to 70 pounds per square inch (psi).

The maximum permissible pressure, according to the plumbing code, is 80 psi. Unfortunately, many homes have excessively high water pressure, and levels above 120 psi can cause a TPR valve to leak.

If high pressure is the problem, you should install a pressure regulator on your main water line or replace the existing regulator if you already have one. And keep in mind that a 7-year-old water heater is nearing the end of its expected life. Yours may soon need replacement.

To write to Barry Stone, please visit him on the Web at www.housedetective.com.

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