Which device initiates the burner motor when a thermostat calls for heat in an oil burner?

• A. Cad cell
• B. Thermostat
• C. Primary control
• D. Draft inducer

Answer: (C)

When a thermostat calls for heat, the signal is sent to the system’s primary control. The primary control acts as the sequence manager for the oil burner: once it receives that heat call, it energizes and starts the burner motor (along with the fuel pump and ignition sequence) and then oversees flame sensing and safety checks. The thermostat itself just initiates the call; it doesn’t directly power the burner motor. The cad cell is the flame detector used after ignition, and the draft inducer provides the necessary draft for combustion, but neither initiates the burner motor.