Water Heater Pressure Relief Valve

Marine Water Heater, Model 1700 Pressure Relief Valve.

Water Heater Pressure Relief valve. Water heater temperature and pressure relief valves, or T&P valves, are a safety feature found on all tank water heaters...

It's designed to open temporarily and discharge short spurts of water when the temperature exceeds about 210 degrees F, and it releases pressure if the tank gets above 75 psi.