Which component serves as the output of the high limit relay in automatic boiler controls?

The output of the high limit relay in automatic boiler controls is correctly identified as the control valve. The high limit relay is designed to ensure that the boiler does not exceed a predetermined safe pressure or temperature. When this set limit is reached, the high limit relay activates to disable certain components to prevent overheating or overpressure conditions.

In terms of the boiler's operational control, the control valve is responsible for regulating the flow of steam or water within the system based on the commands received from various control relays, including the high limit relay. When the high limit relay is triggered, it often signals the control valve to adjust its position, effectively managing the thermal load and ensuring safe boiler operation.

While the other components mentioned—such as low limit relays, high pressure relays, and boiler feed pumps—play essential roles in boiler operation, they do not represent the direct output of the high limit relay. The low limit relay typically works in conjunction with the operational baseline to prevent the boiler from dropping below safe operational thresholds, while the high pressure relay monitors excessive pressure situations. The boiler feed pump is responsible for supplying water to the boiler but does not directly respond to the high limit relay's signals. Hence, the control valve stands out as the correct answer.