Lennox: annual boiler servicing, done to the manufacturer's procedure before the season

A boiler's service schedule is published by its manufacturer, and most warranties are written around it: annual service, performed and recorded, by someone qualified to follow the manufacturer's procedure. The annual visit follows that procedure step by step, with combustion measured and adjusted, heat exchanger and burner cleaned, the condensate path cleared, safety devices exercised and venting and gas connections checked, rather than a quick look at whatever is most visible.

Timing is part of the service. Annual visits are scheduled ahead of the heating season, when a fault found in the fall costs little compared with the same fault discovered in a winter cold snap. Each visit ends with a dated service record documenting what was done, which is also the record manufacturers ask for when warranty questions arise.