Arrived on site to provide a second opinion on cracked heat exchanger. Upon arrival we started by turning the gas and power back on to the furnace to perform a combustion analysis. Analysis showed high levels of CO in the flue. Almost 200ppm before the blower came on. This is pretty abnormal for a functioning heat exchanger. We turned off the furnace and removed the gas valve to inspect the burners. The burners were very corroded. We scoped the heat exchanger but could not get all the way around the bends. There were no visible cracks but we performed the lighter test. When the blower came on the lighter flame danced around wildly. The combination of higher than normal levels of CO and the dancing flames leads us to believe the heat exchanger is cracked and the furnace should be replaced. Left furnace inoperable by disabling gas valve, turning off the gas, and removing the disconnect switch.
