What is a potential consequence of having a faulty cad cell?

Having a faulty cad cell can lead to the system starting but then shutting off after a few seconds. The cad cell, or cadmium cell, is a safety device that detects the presence of a flame in the burner. If the cad cell is not functioning properly, it may fail to accurately sense the flame. As a result, when the burner ignites, it might initially operate normally, but once the cad cell is unable to confirm that a flame is present, the safety control system will deactivate the burner to prevent potential hazards associated with a flame failure, such as the risk of uncombusted fuel or an explosion. This is a normal safety feature in oil heating systems to ensure safe operation.

The other choices indicate scenarios that do not typically occur due to a faulty cad cell. For example, the system will not shut down permanently; it can be repaired or replaced. Operating more efficiently or requiring a complete system replacement also do not directly correlate with faulty cad cells. The primary immediate symptom of a fault in the cad cell is the burner starting and then shutting off shortly afterward, which directly relates to the functionality of flame detection and safety protocols in oil heating systems.