Your thermostat may control both your heat and central air, so it´s important to have it operational at all times. If your indoor room thermostat fails, or you wish to upgrade to a digital stat, you can replace it yourself. Hiring an electrician to install one can cost hundreds of dollars depending on hourly rates. With some common household tools you can rewire a new thermostat and snap it back into place in about 10 minutes or less.
Turn off the main power supply to the thermostat. Test the power to the thermostat by turning the heat or air conditioning on full blast.
Remove the cover of the thermostat. Usually the covers simply snap on into place. Some thermostat covers screw onto the housing of the thermostat. If this is the case, simply turn the cover counterclockwise until it comes free from the housing.
Draw a diagram of the wiring, including the colours of the wires and where they connect to the inside of the thermostat housing. A digital camera picture can help replace a drawn diagram.
Open the package of the new thermostat and compare the wire connection placements to ensure your diagram or photo will line up properly. If there is any confusion, refer to the manufacturers phone number in the instruction manual of the new thermostat. Most companies will instruct you in how to rewire the connections.
Remove the wires from the housing of the old thermostat. Most use small screws or push-in connectors to hold them in place. Turning the screws counterclockwise, enough to remove the wire, is all that's necessary. For push-in connectors, simply unplug the wire from the connector.
Use the appropriate screwdriver to remove the screws holding the backing plate of the old thermostat housing once all the wires have been disconnected. Ensure the backing plate of the new thermostat will align to the placement of the old. Otherwise drilling and anchor inserts may be required.
Place the wires through the centre of the new thermostat backing plate, housing and reinstall the screws to hold it to the wall.
Rewire the thermostat housing according to your diagram, photo or instructions from the manufacturing company.
Place the new cover onto the thermostat housing. Turn the main power supply back on to test it.
Make sure the replacement thermostat will fit in place of the old thermostat. Obstacles such as light switches may hinder a larger thermostat from a proper fit.