What safety concern arises if an oil furnace's primary control trips?

When an oil furnace's primary control trips, it indicates that there is a safety issue preventing the furnace from functioning as intended. A critical safety concern in this scenario is the presence of a pool of oil in the firepot. This situation occurs if the oil continues to flow into the combustion chamber without igniting, which can lead to an accumulation of flammable oil.

If there is a pool of oil in the firepot, it poses a significant risk of fire or explosion. The primary control is designed to shut down the furnace to prevent such dangerous conditions, making it imperative to address the underlying cause, such as a faulty ignition system or other malfunctions, to ensure safe operation.

The other options, while they can represent problems that may arise in the furnace system, do not directly correlate with an immediate safety concern resulting from the primary control tripping in the same way that an uncontrolled pool of oil would. Addressing the safety aspect of oil accumulation helps maintain a safe environment around the furnace, underscoring the importance of proper system maintenance and vigilance in monitoring furnace operations.