What might cause a furnace burner to short cycle or regularly shut off on high limit?

A furnace burner short cycling refers to the situation where the burner frequently turns on and off in a short period, often due to a failure to maintain proper operating conditions. This can lead to increased wear and tear on the system and inefficient operation.

The correct choice, which points to dirty air filters restricting airflow, directly impacts the furnace's ability to draw in sufficient air for combustion. When the airflow is restricted, the burner cannot achieve optimal performance, causing it to overheat and trigger the high limit safety feature. This safety mechanism shuts the burner off to prevent damage, leading to short cycling.

While other issues can also cause a furnace to shut off, they do not directly relate to the airflow dynamics as much as dirty filters do. Insufficient water in the system primarily pertains to hydronic systems rather than forced-air furnaces. Incorrect thermostat settings may not prompt the high limit switch to activate, so they wouldn't cause short cycling in a straightforward manner. Low fuel supply can lead to operational inefficiencies, but it typically presents differently than the pronounced effects of restricted airflow, which directly leads to overheating and subsequent shutdowns for safety reasons. Therefore, the choice of dirty air filters is the most accurate in explaining the phenomenon of short cycling in this context.