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The TPR (Temperature and Pressure Relief) valve is located on the top or side of the water heater. It's purpose is to relieve pressure in the event that the thermostat jams and the water heater overheats. Several problems can result from a faulty TPR valve:
- The valve can develop a leak. As they age, the rubber seal can become stiff and brittle. If you see water seeping from the discharge tube then the valve is leaking. It should be replaced by a qualified plumber.
- The valve can fail completely and water gushes from the discharge tube. The water will likely be hot, so extreme caution is advised. Immediately turn off the cold water valve to the heater and turn off the gas or electric power. Have the valve replaced by a qualified plumber.
Note the lack of a discharge tube in the valve in the photo at the lower right. If the valve opens or leaks then hot water will be dumped into the house, attic, or garage where the heater is located. All TPR valves should have a discharge tube that terminates outside the house or into a suitable approved drain receptacle.
If the valve leaks, why not just plug it and forget about it? That's a really BAD idea. The amount of energy contained in 50 gallons of superheated water is tremendous and equal to several sticks of dynamite. If all that energy is released at once, mass destruction and injury can occur.
The Discovery Channel Mythbusters TV show recently had an episode with a segment on what happens if the TPR valve is blocked and the water heater thermostat jams in the on position. It's very dramatic and a great example of why a properly functioning TPR valve and discharge tube is essential. Watch here.
