Arrived at the home for a heater issue. Was greeted by the customer and was shown the furnace and thermostat. The customer stated the heater would not work the night before and wanted it checked to see what was going on. The customer turned the furnace off and let the system set until about 1:30-2:00pm this afternoon. The customer turned the furnace back on this afternoon and she said it seemed to be working at this time. I started looking at the furnace and could not find anything wrong with the furnace, I cycled the system several times and checked the components of the furnace and could not get the system to fault out. Told the customer that if the furnace messes up again to leave the furnace be and call us so we can look at the furnace while it is not running properly.