What could excessive smoke or soot around the burner indicate?

Excessive smoke or soot around the burner is a strong indicator of incomplete combustion, which is commonly tied to a blocked flue vent. When the flue vent is obstructed, it hampers the proper exit of combustion gases, leading to a buildup of unburned fuel and particulate matter. This condition typically results in an increase in smoke and soot production, signaling that the burner is not operating efficiently and may pose safety hazards.

In contrast, normal operation would not produce excessive smoke or soot, while a low oil supply would not typically cause such a buildup but rather lead to inconsistent operation or shutdowns. High combustion efficiency is characterized by clean combustion with minimal emissions, directly opposing the scenario of excessive smoke and soot. Therefore, when assessing burner performance, a blocked flue vent is a significant concern that needs immediate attention.