The oil burner technician should service your oil-fired appliance after each heating season. When he removes the connector pipe and opens the cleanout door, he can find one or more of the following:
New high-efficiency oil-fired appliances require smaller flue sizes than older units. Where an old unit may require an eight-inch flue, the replacement unit’s installation instructions may call for a five-inch flue. This is a 60% reduction in flue size. Couple that with lower flue gas temperatures of new units and the flue size becomes much more critical to the proper operation of the present day oil-fired appliance.
How can these problems be solved?
Retrofitting a chimney with a UL Listed, properly sized and properly installed chimney lining system is the most important and easiest way to prevent these problems.