Which situation indicates that an oil burner requires maintenance?

Frequent soot accumulation in an oil burner is a strong indicator that the system requires maintenance. Soot forms as a byproduct of incomplete combustion, which can occur due to several factors such as improper fuel-air mixture, a dirty burner, or inadequate air supply. Accumulation of soot can not only reduce efficiency but also lead to more serious issues like overheating or even a fire hazard.

In comparison, consistent heat output and flame stability suggest that the burner is operating correctly and efficiently. Clear exhaust emissions indicate clean combustion and typically mean that the burner is functioning well and not producing harmful pollutants. Therefore, it is the presence of frequent soot accumulation that signals the need for maintenance to ensure operational safety and efficiency.