What is the primary function of a flame roll-out sensor?

The primary function of a flame roll-out sensor is to protect against overheating. This device is designed to detect the presence of flame where it should not be, specifically in areas close to the combustion chamber or heat exchanger. If the flame rolls out due to a blocked vent, improper airflow, or a malfunction in the system, the sensor will activate to shut down the burner. This is critical because uncontrolled flame roll-out can lead to serious overheating, which poses a fire hazard and can damage the heating system itself.

In a well-functioning system, the flame roll-out sensor acts as a safety mechanism to ensure safe operation and to prevent dangerous conditions that could arise from flame misplacement. The other options—monitoring airflow, detecting flame presence, or ensuring proper gas flow—while important for overall system function and safety, do not encapsulate the specific role of protecting against overheating that the flame roll-out sensor directly fulfills.