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 7.2%o2 1ppm co 0 smoke While performing g the maintenance we found the burner coupling was starting to get stripped and was showing signs of wear. Brought the issue to the customer’s attention. After getting customer authorization we replaced the burner coupling. Unit is working properly.