I have a trane xb90 furnace which by looking at the red light on the furnace indicates that it is working fine. But I have the thermostat set at 68 and its now around 60 degrees. So I would guess that maybe its the internal circuit board not communicating with the furnace. I had that replaced two years ago. Any thoughts, comments, suggestions would be appreciated
First, bypass the thermostat as the possible cause by..
turning off the furnace power/ remove the stat wires from their R & W connections in furnace/ jumper R & W connecters together/ turn power back on.