Performed pm on oil furnace 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 While performing the maintenance we found the flue pipe is starting to corrode and get very brittle. Recommend replacing the flue pipe before holes develop. Found a bird in the flue pipe. Recommend having chimney inspected. 2 lengths of 6 inch a 5-6 reducer 6 inch T