What could be a sign of incomplete combustion in an oil burner?

Excessive smoke production is an indicator of incomplete combustion in an oil burner. When an oil burner operates efficiently, it should convert the fuel into energy without leaving a significant amount of unburned fuel or particulates in the flue gases. Incomplete combustion typically occurs when there is not enough air for the fuel to burn completely, resulting in the release of soot and smoke. This smoke is primarily composed of unburned hydrocarbons and particulate matter, which are signs that the combustion process isn't functioning optimally.

On the other hand, clear flue gases would suggest that the combustion is complete, with minimal pollutants and residues present. High efficiency ratings imply that the burner operates effectively, maximizing fuel usage and minimizing waste. No pressure fluctuations typically indicate stable operation; thus, they would not be associated with combustion issues.