What could cause a high-temperature rise through a furnace?

A high-temperature rise through a furnace can occur due to several contributing factors, all of which are addressed in the choice that states "All of the above."

When there is too much gas pressure, the furnace may burn fuel too rapidly, leading to excessive heat being generated. This condition can create a situation where the temperature exceeds normal operational levels, causing a high-temperature rise.

Similarly, a dirty filter can significantly restrict airflow. When airflow is reduced, the furnace may struggle to provide adequate ventilation for the combustion process. This not only affects efficiency but can also lead to overheating if the heat exchange process is disrupted.

Air flow problems encompass a broad range of issues, such as duct blockages or fan malfunctions, which can similarly cause the furnace to overheat. Inadequate airflow prevents the furnace from effectively distributing heat, leading to higher temperatures in the furnace itself.

When all these factors are considered together, it is clear that each one can independently or collectively lead to an increased temperature rise through the furnace, thereby warranting the conclusion that multiple issues—too much gas pressure, a dirty filter, and airflow problems—can combine to create significant performance concerns within a heating system.