Call back. We were out yesterday for a no heat complaint on the main floor. Customer states heat went out again. Arrived and found the thermostat showing a call for heating but neither the furnace nor the blower were running. At the furnace, I found the control board indicating no call for heat, but also resetting itself. Confirmed a call for heating at the control board. Control board should be replaced. Looking at the last 6 faults on the control board indicates multiple high limit faults indicating the furnace may be overheating. The examination of all of the components indicate the return ducting is significantly undersized for the size of the furnace as well as the tonnage of AC installed. There are currently 2-12” and 1-10” return ducts installed with lengths extending well past 50 foot. In total less than 1200 CFM given extended lengths and tight bends. The gas furnace loan should have a minimum of 1800 CFM and the cooling capacity at 3 1/2 tons equals a minimum of 1400 CFM.