Responded to no heat call for 16-year-old Gibson high efficiency furnace that was operational upon arrival. System diagnostics revealed intermittent operation with burning smell. After multiple test cycles, identified furnace tripping on high limit switch. Performed comprehensive system check: verified gas pressure, inspected A-coil, filter, heat exchanger, combustion process, blower motor, and exhaust fan - all functioning properly. Determined failing high limit switch as root cause. Replaced high limit switch, restoring proper system operation and safety parameters.
