The primary control must be capable of responding to which condition?

The primary control in heating systems, particularly those using oilheat, is a crucial safety component designed to monitor and ensure the safe operation of the burner. It must be capable of responding to the presence or absence of a flame to prevent dangerous situations such as the potential accumulation of unburned fuel, which can pose safety hazards like explosions or fire.

When the primary control detects a flame, it allows the burner to continue operating. Conversely, if it fails to detect a flame, it will shut down the burner to stop the fuel flow, thereby mitigating the risk of hazardous conditions. This critical function underscores the importance of flame detection in maintaining safe and efficient operation of heating systems.

The other options, while related to the operation of a heating system, do not represent the primary function of the control. Temperature of the motor, fuel level in the tank, and the load on the motor are important, but they are not the primary factors that the main control system is designed to monitor for safety and operational integrity.