The solenoid valves in the fuel oil supply line to an automatically fired auxiliary boiler, are automatically closed by __________.

Correct Answer: Option C — high steam pressure

Automatic auxiliary boilers use pressure-actuated switches. When steam pressure reaches the upper limit, the control circuit de-energizes the fuel supply solenoid valves to halt combustion, protecting the pressure vessel from over-pressurization per 46 CFR Subchapter F standards.