Diagnosed Bryant 925SA furnace with intermittent operation. Found corroded flame sensor causing improper flame rectification (0.5 microamps measured). Replaced sensor and verified proper signal at 3.2 microamps. Also discovered partially blocked condensate trap causing pressure switch to open during operation. Cleaned trap, verified proper condensate drainage, and measured draft inducer vacuum at -1.2 inches WC. Advised homeowner on importance of annual maintenance and proper humidifier settings during spring transition.