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. 7.1% o2, 21 ppm, 84.0% efficient System is operating properly. Removed and installed a new backflow preventor/ auto feed combo. Opened valves and adjusted the water pressure. The boiler is getting up there in age(approx 1996). The boiler is a steel boiler which are normally rated for about 15 yrs.