One of the main reasons your boiler could be smoking is because it is in need of professional repair. The boiler can produce black smoke, white smoke or even a light gray smoke when it is not running correctly.
The boiler repair technician can adjust the air flow and fuel settings on the burner so it will run correctly and no longer smoke. If the oil burner is putting out a dark black smoke it could be because the burner is running to rich and needs to be adjusted so it will run leaner.
There are a number of reasons why the oil burner or boiler can smoke including clogged burner nozzles, incorrect air flow intake settings, bad electrodes, improper venting and many other things. You should not try to repair an oil burner or furnace yourself unless you are properly trained to do so. The licensed oil burner tech will come to you home or place of business with all of the tools that will be needed to diagnose and troubleshoot the problem with your oil burner or boiler. The boiler technician can then replace the need parts and adjust the intake settings to make sure that the boiler is running at the most efficient setting possible so you can have a 100% reliable furnace throughout the heating season.
You can call a boiler technician and tell them that your boiler is smoking and then provide them with your address and they will come out to fix it for you. They may require you to be home at the time of repair. It is very important that you call someone that is licensed to fix your boiler as soon as you see it smoking. Its not a good idea to keep a boiler in use for an extended amount of time if it is not running properly. You might want to ask your local boiler repair company if they offer a winter service contract that will cover future repairs if you should need them.