The customer contacted me because their furnace was blowing cold air, leaving their home uncomfortable. I started by checking the thermostat settings and inspecting the system components, using my multimeter to test the ignition system. I discovered a faulty igniter that was preventing the furnace from igniting properly. After replacing the igniter and ensuring all connections were secure, I ran the furnace through a full heating cycle to confirm it was working correctly. The heating was restored, and the customer was relieved to have warmth back in their home.