The T & P valve, which stands for temperature and pressure relief valve, is a safety device that protects against excessive temperature and pressure levels in the water heater. The valve is located on or near the top of the tank. Part of the valve extends into the unit.
If water discharges, it usually means the valve is defective (it opened and didn’t close) or the water heater is operating under too high a temperature or pressure.
First, check the water temperature and make sure the setting is about 120 degrees F (or “medium” if your thermostat doesn’t have a degree reading). If the valve continues to leak, remove it and examine it for mineral buildup and signs of corrosion. The minerals in especially hard water can clog it or attack the metal parts, resulting in valve failure. This is especially common with water from a well. And if you have municipal water, check with your local water department to find out if the water supply has a high concentration of minerals. In either case, you’ll have to soften your water.
If the valve looks clean, consider two other possible causes: high water pressure in the municipal system or some sort of backflow preventer around the water meter or main shutoff. You’ll need a licensed plumber to diagnose and handle these problems.
You’re supposed to flush your water heater regularly to remove sediment from the bottom of the tank. But many homeowners don’t do it until they hear rumbling from the tank. After the flush, they discover that the drain valve leaks. If the drain valve is brass, you can usually replace the washer. It’s a fairly easy but time-consuming fix because you have to shut off the water and drain the tank. If you have a plastic drain valve, your best bet is to replace the entire valve. You guessed it; you’ll have to drain the tank for that fix, too. So how do you stop the drip until you get around to fixing the valve? Simple—buy a brass garden hose end cap and screw it onto the valve threads.