What component starts the burner motor on an oil burner when there is a call for heat?

The component that initiates the burner motor on an oil burner when there is a call for heat is the primary control, which manages the burner operation including the ignition sequence. The primary control ensures that power is sent to the burner motor when the thermostat signals a demand for heat, effectively starting the heating process.

The cad cell primary control, which detects the presence of a flame, is also a crucial part of the system as it ensures that the burner operates safely by confirming that there is a flame once the burner has started. If no flame is detected, the cad cell will interrupt the operation to prevent unsafe conditions.

Both the primary control and the cad cell function together to start the burner motor and ensure safe operation after ignition. Therefore, the option that includes both the primary control and the function of the cad cell is comprehensive, as both components play a key role in the oil burner operation process. This coordination allows a reliable start and safe function of the heating system, making this answer the best choice.