Which device is responsible for automatically shutting off fuel if the flame is lost?

• A. Control electronics
• B. Gas regulator
• C. Fuel source
• D. Flame sensor

Answer: (D)

A flame safety system hinges on confirming flame presence through a flame sensor. This sensor, often a thermocouple or flame rod, is heated by the flame and provides a continuous signal indicating that combustion is occurring. If the flame goes out, that signal drops or disappears, and the safety control responds by shutting off the gas valve to prevent fuel from leaking into the system. The control electronics coordinate this response, but the actual automatic shutoff is driven by the flame sensor detecting the loss of flame. The gas regulator simply controls pressure, and the fuel source supplies the gas; neither by itself detects flame loss or initiates the shutoff.