Performed diagnostic on 12 year old system. This is a furnace only no AC. Homeowner states that her system is working fine and is heating fine. The only issue is that the temperature on the thermostat does not what to what she set it through and will change throughout the day. Thermostat in the home is a programmable thermostat and it was resorting back to the schedule throughout the day. Showed homeowner how to set a temperature and hold it so that it will not change throughout the day. Had homeowner do it on her own and she fully understands how to work thermostat. System is operational upon departure.