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 4.8%o2 6ppm co 0 smoke While performing the maintenance we found high levels of sludge at the oil filter canister. After getting customer authorization we added a sludge additive to the oil tank. Also found 2 hi-vents had been leaking in the past and were showing signs of corrosion. After getting customer authorization we replaced the 2 hi-vent Drained pressure from the system. Removed 2 old hi-vents and installed 2 new hi-vents. Filled system back up with water and purged air out of all zones. Started and tested both zones. Had hot water coming back at the return. When leaving boiler pressure was at 20psi when leaving. Unit is working properly.