Cad cell primary control uses a cad cell to perform which action?

• A. To prove ignition
• B. To detect flame
• C. To regulate air
• D. To measure temperature

Answer: (A)

The main idea is that this device acts as a flame-sensing safety check. A cad cell is a flame detector: after ignition is attempted, the cad cell looks for the presence of flame and sends a signal to the primary control. If flame is detected, the control knows ignition succeeded and continues supplying fuel. If no flame is detected, the control shuts down the ignition attempt to prevent unburned gas from accumulating. This is not about adjusting air flow or measuring temperature; it’s specifically about proving that ignition has occurred.