TPR Valve

A TPR valve combines two independent relief mechanisms in one cartridge: a temperature-sensing element that opens at 210°F and a pressure-sensing element that opens at the tank's rated pressure (typically 150 psi). Either trigger fires the valve. The valve sits on the hot water tank (usually upper third) with a discharge line running down the side or to a floor drain—never capped or reduced in size.

In the field, a weeping TPR is almost always a sign the tank's internal pressure or temperature has climbed past normal. Common causes: a bad dip tube allowing cold water to mix at the thermostat, a stuck thermostat ramping heat too high, or a faulty pressure relief valve on an expansion tank that's forcing backpressure into the supply line. Sediment buildup can also trigger relief cycling if the tank gets hotter at the burner than the thermostat intends.

Code requires TPR valves on all storage water heaters and on sealed expansion tanks. The discharge line must be sized per manufacturer spec (usually 3/4" min), slope downward, terminate at least 6 inches above the floor or drain, and must not create back-pressure. A leaking TPR almost never means the TPR itself is bad—fix the root cause or you'll just replace it again.