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 8.5%o2 25ppm co 0 smoke Noticed higher than normal levels of sludge. Recommend getting oil sludge additive. Also found high levels of corrosion around the domestic water coil. Boiler is from 2000. Recommend replacing the boiler in the near future. Customer stated they heard air in the 2nd floor zone. Bled 2nd floor zone until all air was out. Started and tested the heat. Had hot water coming back to the return. When leaving boiler pressure was