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 7.8%o2 3ppm co 0 smoke While performing the maintenance we found the porcelain on the nozzle assembly was broken and missing a very large section. After getting customer authorization we replaced the porcelains with new ones. Started and tested the system.