Performed a heating pm on (2) oil boilers. Brushed and vacuumed. Replaced the oil filters, nozzles and strainers. Started and checked the safeties. Performed a combustion test. Main house-6.7% o2, 21 ppm, 83.4% efficient Rear house- 5.4% o2, 29 ppm, 84.9% efficient System is operating properly.