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 5.4%o2 23ppm co 0 smoke While performing the maintenance we found that there was air in the lines. Notified the customer and recommended purging the zones. After getting customer authorization we purged both zones of all air. Started and tested the boiler and had hot water coming back. Boiler pressure when leaving was 18/19