Arrived onsite to fix leaking humidifier supply valve and diagnose furnace heating issue. For the humidifier, found a second supply valve on the system that isn’t leaking. Turn that valve on and confirmed operation of the humidifier. Performed diagnostic on furnace. Furnace is overheating and going off on high limit. Confirmed limit switch is working. Measured temperature rise at 70-80 degrees. Well out of range. Performed inspection of heat exchanger using camera probe. May have cracks in heat exchanger but inconclusive findings. Attempted running furnace without filter to increase air flow but furnace still running hot. Next steps is to retest system with combustion analyzer to determine if there is CO in air stream which would indicate cracked heat exchanger.
