(A) The maximum allowable working pressure of a boiler carrying the ASME Code symbol must be determined by the applicable sections of the code under which it was constructed and stamped. Subject to the concurrence of the department, the boiler may be re-rated in accordance with the rules of a later edition of the ASME Code and in accordance with the rules of the National Board Inspection Code.

(B) The maximum allowable working pressure of a boiler which does not carry the ASME or the API-ASME Code symbol must be computed in accordance with the Inspection Code of the National Board of Boiler and Pressure Vessel Inspectors.

(C) This chapter must not be construed to prevent the use, the sale, or the reinstallation of a boiler referred to in this section if the boiler has been made to conform to the regulations of the department governing existing installations and has not been found upon inspection to be in an unsafe condition.