purchased in 2005 and has been flawless until late last season. If I start it at say 66 degrees it stays for a bit but over the next 12 hours or so it slowly rises to 75 and stays there. Ive changed the ESP and room temp sensor. Any other ideas before I replace the main control board? It runs fine otherwise. Contemplating adding a setback thermostat and switching the igniter switch to manual and letting it go in maintenance mode if the temp is higher than I want. Thanks in advance for any help!!