Performed fall furnace check on 2-year-old Lennox system. During gas pressure adjustment, flame extinguished momentarily with CO levels spiking to 3000 ppm. Immediately shut down system, thoroughly inspected burners and gas pressure components finding no visible issues. Upon restart, system operated normally with all components functioning properly. Blower wheel and control board verified operational. Advised homeowner of incident and recommended vigilance for any recurring symptoms.