Performed a heating pm on an oil boiler. Brushed and vacuumed. Replaced the oil filter, nozzle and strainer. Started and checked the safeties. Performed a combustion test. 4.9% o2, 49 ppm, 0 smoke, 80.9% efficient System is operating properly. Because of how the boiler was originally installed, there is no way to perform a proper cleaning. I am unable to get the back clean out door off. I took the flue pipe off and cleaned the top section of the boiler