A boiler will not fire if the pilot burner or main burner fails to ignite. Key checks include cleaning the pilot nozzle, filter, flame sensor, and ensuring proper electrode gap adjustment. For main burners, inspect rotary cups for damage, clean air passages, verify fuel oil temperature adjustments and solenoid valve functionality. Low efficiency often stems from fouled tube surfaces or combustion control malfunctions; remedies involve water washing smoke sides of tubes or addressing feed water treatment issues. Flame failures can result from low atomizing air pressure or decreased fuel oil pressure—inspect filters and adjust temperatures as needed.