What device is used to relieve excessive pressure within a water heater?

The temperature pressure-relief valve is specifically designed to protect a water heater from excessive pressure buildup. This valve serves a critical safety function by opening automatically when the internal pressure or temperature exceeds predetermined levels, allowing steam or hot water to escape. By doing so, it prevents potential damage to the water heater and reduces the risk of catastrophic failure or explosion.

In contrast, a pressure gauge simply measures the pressure within the system but does not actively relieve it. An expansion tank, while useful in managing pressure fluctuations in a closed system, does not directly relieve pressure in the same manner as a temperature pressure-relief valve. A thermostat controls the water temperature by regulating the heating element but does not manage pressure. Thus, the temperature pressure-relief valve is the essential device for maintaining safe pressure levels within a water heater system.