I am maintaining the Buderus Wall Hung Boiler. Buderus a hi-efficient German boiler This is labor-intensive maintenance. Therefore I take the burner section apart. Then clean out the burners, drain pan, flame sensor, trap, and exhaust. Next, I test the boiler. Afterward, I did a combustion test yet due to video length I didn't include that. Buderus Boilers require yearly service I found out this boiler wasn't serviced last year. Buderus Boilers keep an HVAC tech busy.