Which of the following actions should be taken FIRST when the boiler fires begin to sputter due to water in the fuel oil?

Correct Answer: Option D — Shift to the settler high suction valve.

Water in fuel oil typically settles at the bottom of the tank. Shifting to the high suction valve draws fuel from the upper portion of the settler, which is less likely to contain water or sediment. This immediate action prevents flame instability and potential boiler flame-out during critical operations.