What is caused by dirty or damaged nozzles?

Dirty or damaged nozzles disrupt the proper atomization of fuel in an oil burner. When the fuel is not atomized correctly, it leads to incomplete combustion, which results in the formation of carbon deposits. These deposits can accumulate on various components of the burner and in the combustion chamber, negatively impacting performance and efficiency.

In contrast, the other choices don't accurately reflect the consequences of dirty or damaged nozzles. Fuel combustion should ideally be efficient and complete, which is hindered by the condition of the nozzle. Improved efficiency would not be achieved under these circumstances, as malfunctioning nozzles directly correlate with reduced efficiency in the combustion process. Lastly, while heat exchange is a necessary function of the system, it becomes ineffective if the combustion process is impaired due to nozzle issues. Thus, the clear consequence of malfunctioning nozzles is the build-up of carbon deposits.