(1) The maximum allowable working pressure of a boiler built in accordance with the A.S.M.E. boiler and pressure vessel code shall in no case exceed the pressure indicated by the manufacturer's identification stamped or cast on the boiler or a plate secured to it.

(2) The maximum allowable working pressure on the shell of a nonstandard, riveted heating boiler shall be determined in accordance with section 9-4-114 (1) covering existing power boiler installations. In no case shall the maximum allowable working pressure of a steam-heating boiler exceed fifteen pounds per square inch gauge, or a hot-water boiler exceed one hundred sixty pounds per square inch gauge, at a temperature not exceeding two hundred fifty degrees Fahrenheit.

(3) The maximum allowable working pressure of a nonstandard steel or wrought-iron heating boiler of welded construction shall not exceed fifteen pounds per square inch gauge. For other than steam service, the maximum allowable working pressure shall be calculated in accordance with the rules for construction of low-pressure heating boilers of the A.S.M.E. boiler and pressure vessel code.

(4) The maximum allowable working pressure of a nonstandard boiler composed principally of cast iron shall not exceed fifteen pounds per square inch gauge for steam service or thirty pounds per square inch gauge for hot-water service.

(5) The maximum allowable working pressure of a nonstandard boiler having cast-iron shell or heads and steel wrought-iron tubes shall not exceed fifteen pounds per square inch gauge for steam service or thirty pounds per square inch gauge for water service.

(6) A radiator in which steam pressure is generated at a pressure of fifteen pounds per square inch gauge or less is a low-pressure boiler.

(7) Each steam-heating boiler shall have one or more officially rated valves of the spring pop-type adjusted to discharge at a pressure not to exceed fifteen PSI. The safety valves shall be arranged so that they cannot be reset to relieve at a higher pressure than the maximum allowable working pressure of the boiler.

(8) No safety valve for a steam-heating boiler shall be smaller than three-fourths of an inch except in case the boiler and radiating surfaces are a self-contained unit.

(9) The safety valve capacity for each steam-heating boiler shall be such that with the fuel-burning equipment installed the pressure cannot rise more than five pounds above the maximum allowable working pressure.

(10) Each hot-water boiler shall have not less than one officially rated pressure relief valve set to relieve at or below the maximum allowable working pressure of the boiler. Each hot-water supply boiler shall have not less than one officially rated relief valve or not less than one officially rated pressure-temperature relief valve of the automatic-reseating type set to relieve at or below the maximum allowable working pressure of the boiler. Relief valves shall be so constructed that they cannot be reset to relieve at a higher pressure than the maximum permitted pressure.

(11) Seats and discs of safety relief valves shall be of material suitable to resist corrosion. No materials subject to deterioration or vulcanization when subjected to saturated steam temperature corresponding to capacity test pressure shall be used in any safety relief valve.

(12) No safety relief valve shall be smaller than three-fourths of an inch nor larger than four and one-half inches pipe size.

(13) When the size of the boiler requires a safety relief valve larger than four and one-half inches in diameter, two or more valves having the required combined capacity shall be used.

(14) Each steam-heating boiler shall have a steam gauge connected to its steam space, or to its water column, or to its steam connection. The gauge or connection shall have a siphon or equivalent device which will develop and maintain a water seal that will prevent steam from entering the gauge tube. The connection shall be so arranged that the gauge cannot be shut off from the boiler except by a cock placed in the pipe at the gauge and provided with a tee or lever handle arranged to be parallel to the pipe in which it is located when the cock is open.

(15) Each hot-water heating boiler or hot-water supply boiler shall have a pressure or altitude gauge connected to it or to its flow connection in such a manner that it cannot be shut off from the boiler except by a cock with tee or lever handle placed on the pipe near the gauge. The handle of the cock, when the cock is open, shall be parallel to the pipe in which it is located.

(16) The scale on the dial of the pressure or altitude gauge for a hot-water heating boiler shall be graduated to not less than one and one-half nor more than three times the maximum allowable working pressure.

(17) The scale on the dial of a steam-heating boiler gauge shall be graduated to not less than thirty PSIG nor more than sixty PSIG, and travel of the pointer from zero to thirty PSIG pressure shall be at least three inches.

(18) In addition to the mandatory requirements for a pressure relief device, each hot-water heating or hot-water supply boiler shall be fitted with a temperature-actuated control, which will control the rate of combustion to prevent the temperature of the water from rising above two hundred fifty degrees Fahrenheit at or near the boiler outlet. The control shall be constructed so that it cannot be set or reset to permit operation of the firing equipment when the temperature of the water is higher than two hundred degrees Fahrenheit.

(19) When a pressure-actuated control is used on a steam-heating boiler, it shall operate to prevent the steam pressure from rising above fifteen PSIG.

(20) Each automatically fired steam or vapor-system heating boiler shall be equipped with an automatic low-water fuel cutoff, so located as to automatically cut off fuel supply when the surface of the water falls to the lowest safe water line.

(21) Each steam-heating boiler shall have one or more water-gauge glasses attached to the water column or boiler by means of valved fittings with the lower fitting provided with a drain valve of the straightway type with opening not less than one-fourth inch diameter to facilitate cleaning. Gauge-glass replacement shall be possible under pressure.

(22) If, in the judgment of an inspector, a steam-heating or hot-water supply boiler is unsafe for operation at the pressure previously approved, the pressure shall be reduced, proper repair made, or the boiler retired from service.