Tom M. 1-17-25 blue shield maintenance. Furnace and Ac 07. Cleaned flame sensor set gas pressure. Idm amps .7. While inspecting the heat exchanger I noticed it has multiple cracked in multiple spots and also has a hole. Carbon monoxide level in the flue is at an unsafe level as well at 175 ppm. I have shut the furnace off and recommended not using it. Customer has signed an unsafe appliance form. He stated he has insurance on his system through State Farm and is going to contact them and get back with us. I’ve provided a price to repair along with labor due to the difficulty of the repair. I recommended upgrading the furnace due to being past its typical life expectancy. Overall condition and efficiency.