Upon arrival homeowner stated she had been feeling symptoms of carbon monoxide poisoning, checked co levels before turning system on 0ppms checked co levels after turning system on and was getting 1ppm. Scoped heat exchanger and found crack on upper cell, tagged furnace and informed homeowner of the potential danger running system in heat mode at this time. Also found gas leak before the meter. Told homeowner she would have to get her gas company to fix it due to it being at the meter. Homeowner decided to have comfort advisor come out tomorrow 1-2. Photos and videos attached.