What device will shut down an oil burner if it detects no visible flame?

The device that effectively shuts down an oil burner upon detection of no visible flame is the flame sensor. A flame sensor is a critical safety component in oil-burning appliances. Its primary function is to monitor the presence of a flame during the combustion process. If the flame goes out for any reason—such as a mechanical failure or fuel interruption—the flame sensor will act quickly to cut off the burner, preventing unsafe conditions such as fuel accumulation or potential explosions.

In contrast to the flame sensor, a thermostat is designed to regulate and maintain a desired temperature by controlling the overall operation of the heating system but does not directly monitor flame presence. The photoelectric cell is typically used in gas burners, specifically to detect light emitted by a flame, which may lead to confusion with its function. Lastly, a gas valve controls the flow of fuel to the burner, but it does not have the capability to detect whether there is a flame present or not. Thus, the flame sensor is essential for ensuring safe operation by providing immediate shutdown in the absence of a flame.