Invoice Summary Performed annual maintenance on Navien NCB-190/080H-NG combi boiler. Inspected venting, combustion air intake, and all connections for leaks or blockages. Inspected and cleaned as needed burner assembly, flame sensor, and heat exchanger. Flushed domestic hot water heat exchanger to remove scale buildup. Cleaned water inlet filter, heating return filter, and condensate trap/line. Checked expansion tank, system pressure, and all safety devices. Verified proper operation of pumps, controls, and thermostat. Ran system in both heating and hot water modes; all readings normal at completion. Verified all rads are heating and there is no air in the system. System operating normally at this time.