Jake K. I arrived for a blue member no heat call. I first spoke with the wife and found that the system stopped heating last night. She showed me the thermostat and I found the thermostat to not be on its base properly. I correctly mounted the thermostat and inspected the unit in the attic. I checked the evaporator coil and found it to be clean and the system to cycle on when I bypassed the thermostat. I then checked the gas pressure amp draws and all electrical components and found it to be working properly. I did find the duct work to be undersized and this can cause some issues if the system can’t move air properly. The husband then got home and met me in the attic. At this time the furnace has been running and we cycled the system off and turned it on at the thermostat. The system came on and ran per the thermostat demands. I did explain that the system has undersized duct work and that it can be causing issues on a colder day if the system can’t breathe properly. The homeowner is