Replacing an old White–Rodgers thermostat with a new one will ensure you have the most up-to-date electronic control over your furnace. The thermostat is the control module that not only allows you to control the temperature, but tells the furnace when it needs to come on to heat the home. If the thermostat fails to work properly, you either waste energy by allowing the furnace to run too much, or your home runs very cool because the furnace does not run enough.
Pull the cover off the old thermostat and remove the captive screws that secure the base plate to the wall with a screwdriver. Remove the screws from the switching sub base to expose the wires connected to the back of the thermostat.
Label each wire before disconnecting it form the old thermostat. Loosen the screw terminals and pull each wire off the thermostat.
Pull the thermostat body off the thermostat base with your fingers. Do not pry the pieces apart or you will damage the unit.
Place the base over the hole in the wall and mark out the mounting locations. If possible, use the mounting locations for the old thermostat.
Drill the mounting holes into the wall with a hand drill and drill bit that measures half the diameter of the mounting screws.
Mount the base plate to the wall with the supplied screws and a screwdriver.
Mount the screws to the terminal screws on the back of the thermostat body. Follow the color code you marked on the wires. Double-check each screw with the screwdriver to ensure you got the screws tight.
Press the excess wire back into the wall. If the hole inside the wall has no insulation in it, pack the hole with approved insulation.
Press the thermostat body onto the base plate.