Performed pm on oil boiler 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 8.4%o2 0 ppm While performing the maintenance we found extremely high levels of sludge and rust buildup at the oil filter canister. The entire canister was full of sludge and sediment. Had to blow out the oil line to get oil flowing into the new oil filter. Recommend getting a sludge additive for the oil tank.