Brushed and vacuumed flue pipe and heat exchanger Replaced oil filter, nozzle, and strainer Checked all electrical connections and safeties Performed combustion and smoke tests 6.9%o2 0 ppm co 0 smoke While performing the maintenance we found the oil line is starting to corrode. Since the oil line is in the concrete the lime in the concrete is starting to oxidize the copper. Would recommend replacing the oil line in the near future. Also found the water heater is from 2014. Would recommend replacing that in the near future as well. Typically recommend replacing water heaters every 10 years. Had to cut the metal on the furnace where the oil line enters since we could not remove the strainer housing. Made the hole larger and now the strainer can be easily removed. Oil line is roughly 20 feet