Which condition must be met to ensure a steam boiler operates efficiently?

To ensure a steam boiler operates efficiently, it is essential for it to have a continuous water supply. This is because the effectiveness of a steam boiler hinges on the availability of water to generate steam. If the water supply is interrupted or insufficient, the boiler can overheat, leading to potential damage and unsafe operating conditions. A continuous supply of water allows for consistent steam production, which is vital for maintaining pressure and heat levels, thus ensuring efficient operation.

Operational conditions that allow for hot water or steam generation hinge on the water level being suitable at all times. Adequate water not only contributes to the efficiency of steam generation but also assists in heat transfer within the boiler system.

The other conditions—operating only when full, turning off burners during operation, or requiring a manual shut-off—do not directly correlate with the fundamental requirement of efficient steam production, which relies heavily on maintaining the correct water level throughout operation. These aspects may pertain to operational safety or controls but do not address the core function of water supply necessary for efficient steam boiler performance.