Responded to no-heat call for 12-year-old furnace that was blowing cold air with pressure switch error code. Diagnosed primary issue as tripped limit switch due to plugged air filter. Reset limit switch and discovered sock lodged in blower assembly near heat exchanger, which was removed after pulling the blower. Inspection revealed heat exchanger showing significant wear - no immediate holes or cracks detected but system is approaching end of service life. Customer advised of findings and scheduled follow-up consultation.
