Responded to no heat call for aging Gibson furnace. Diagnosed system was operational upon arrival; customer had already addressed two issues by removing obstruction from intake and replacing severely clogged filter. Performed preventative maintenance including flame sensor cleaning, electrical component inspection, and condensate drain clearing. Identified severely corroded water heater venting requiring immediate attention; tagged water heater as unsafe. Recommended replacement control board and igniter as preventative measures based on furnace age and type.
