Temperature and pressure relief valves (or combinations thereof) and energy cutoff devices shall bear the label of an approved agency and shall have a temperature setting of not more than 200°F (93.3°C) and a pressure setting not exceeding the tank or water heater manufacturer's rated working pressure. Where a pressure rating of more than 150 psi (1034.25 kPa) is not necessary for the proper function of the domestic hot water system, the pressure rating of the relief valve shall be limited to 150 psi (1034.25 kPa). The relieving capacity of each pressure relief valve and each temperature relief valve shall equal or exceed the heat input to the water heater or storage tank, and shall have the AGA steam temperature rating clearly indicated.