T&P Relief Valve (TPR)
A safety valve on every tank water heater that releases water if temperature or pressure climbs too high, preventing the tank from rupturing or exploding.
The temperature and pressure relief valve, mounted on the top or upper side of a tank water heater, is the device that keeps a water heater from becoming a hazard. If the water exceeds about 210 degrees or pressure passes roughly 150 PSI, the valve opens and dumps water down a discharge pipe to relieve the buildup. Without it, a runaway thermostat could turn a tank into a pressure vessel with enough stored energy to do serious damage, which is exactly why code requires one on every tank.
A TPR valve should be tested periodically by lifting its test lever and letting water flush through the discharge pipe. Two failure modes are common. A valve that weeps or drips steadily often signals real trouble upstream, frequently thermal expansion in a closed system, and points to a needed expansion tank rather than just a new valve. A valve crusted shut by mineral buildup is the dangerous case, because it has quietly lost its ability to open when it must.
The discharge pipe matters as much as the valve. Code requires it to run down to within a few inches of the floor or to a drain, so escaping scalding water and steam are directed safely rather than spraying a person. A missing, capped, or improperly routed discharge tube is one of the most common items an inspector flags, and a homeowner should never plug a dripping valve, the drip is information, not a nuisance to silence.
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