What is a common symptom of a malfunctioning fuel oil burner?

Intermittent ignition is a significant indicator of a malfunctioning fuel oil burner. This issue often arises from various factors, such as improper combustion air levels, fuel viscosity, or mechanical faults within the burner system. When ignition is inconsistent, it can lead to inadequate heating, increased emissions, and potential safety hazards due to the risk of unburned fuel accumulating.

The other choices highlight aspects that do not typically indicate a malfunctioning burner. A constant flow of oil can suggest that the burner is functioning to deliver fuel, while a stable flame temperature indicates that the burner is operating efficiently. Increased ash production is more commonly associated with solid fuel systems rather than fuel oil burners, and it does not directly relate to the ignition process. Thus, intermittent ignition stands out as a clear symptom of a problem needing attention in a fuel oil burner system.