A homeowner called because their furnace would ignite for a minute then shut off before the house could warm up, causing concern as the September nights began to get cooler. Upon arrival, I observed the heating cycle and diagnosed a dirty flame sensor, a common issue that prevents the system from confirming a stable flame. After safely shutting down the unit, I removed, cleaned, and reinstalled the sensor. I then ran a full diagnostic cycle, and the furnace ignited and continued to run perfectly. The customer was thrilled it was a quick and simple repair and is now confident their furnace is ready for the upcoming winter.