Arrived to remedy an inoperable system. Upon inspection of the system, found the furnace displaying no fault code. Is displaying an idle code. This tells me that the furnace is not receiving any signal from the thermostat. Performed diagnostic on the thermostat and verified that it is failed. Spoke with homeowner about thermostat replacement solutions. With homeowners approval installed a new thermostat and ran through the programming options. Set up the schedule for both heating and cooling. System is functioning properly at this time.