Install a new programmable thermostat by turning off the power, removing the old unit, installing the new wall plate and transferring the wires to the new device. Snap the new thermostat into the wall plate. Some thermostats require batteries to operate.
Before attempting to install a new thermostat, the owner should read the manufacturer's directions that accompany the new unit. Installation instructions sometimes vary. The owner should also turn off the power at the electrical panel for the furnace and air conditioning.
Older thermostats usually snap off the wall plate. Once the unit is off the wall, snap a photo of the connections before removing any wires. After removing the wires from the terminals, tie a large loop on the cord to prevent it from falling back into the wall. Remove the old wall plate.
If the new thermostat includes a wall plate, attach it to the wall. It is sometimes necessary to use screw anchors or drill new holes to attach the wall plate. Consult the photo of the back of the thermostat, and connect the wires to the new thermostat. Connect each wire to the screw with the same letter code as the old unit, and ignore any color codes. Install any required batteries, and snap the new thermostat into place.