46 CFR §53.05-2

1. (a)Relief valves. The relief valve requirements for hot water boilers must be as indicated in article 4 of Section IV of the ASME BPVC (incorporated by reference; see § 53.01-1) except as noted otherwise in this section.
2. (b)Hot water heating boilers. Each hot water heating boiler must have at least one safety relief valve.
3. (c)Hot water supply boilers. Each hot water supply boiler must have at least one safety relief valve and a temperature relief valve or a pressure-temperature relief valve. The valve temperature setting must not be more than 99 °C (210 °F).