Home Repair: How to Replace Your Home Thermostat

Homes are supposed to stay warm in winter and cool in summer when everything works right. The brain that drives this system in most homes is a simple device called the thermostat. While more sophisticated ones have been developed over the years with programs and timers, the idea behind the device is still the same.

Thermostats all have some form of internal switch that completes an electrical circuit.

When the temperature hits the preset points, your heating or cooling system is engaged to return the temperature to the desired level.. When the thermostat fails, the entire system stops working. The good news is that thermostats in most homes are relatively easy to replace.

The complexity of the thermostat have little to do with the process to replace it.

To control your heating and cooling, the thermostat is attached to several wires (the number can vary from system to system). These wires are color coded with specific colors designating input, output, and type of process being controlled. Here is a list of the terminals that you may see on the interior of the thermostat and the color most often associated with it.

As a general rule, the more common colors are as follows:

R terminal gets the red wire; RC terminal will usually mean red for cooling control, and there may also be a terminal marked RH for heating (red is the incoming power); Y designates the yellow wire and controls the relay for the air conditioner compressor; a Y2 terminal will designate a staged cooling system; W and W2 serve the same purpose for heating as the Y terminals for cooling and receive the white wire; a G terminal gets the green wire; O gets the orange wire (this might be labelled B and get a dark blue or possibly black wire; C will get a neutral colored wire; any other terminals will be specific to your system and need to be referenced in your owners manual.

Depending on the type of wire used by the original installer, the colors may not always match the terminal lettering.

It is best to note the terminal name and wire color attached before removing the old thermostat and follow the same pattern on the new one. Another good idea is to compare the new thermostat terminals to the old thermostat before deinstalling the old unit just to be certain that you can follow the pattern. If you have significant questions, you may need to consult your home center for advice or call in a professional.

Start the replacement by removing the cover of the thermostat.

Usually, this involves gripping the outside of the cover and popping it off of the unit. Check for screws or fasteners before applying too much pressure to prevent damaging the wall by pullng the whole device off instead of the just the cover. Once the cover is off, you may have to remove an interior screw or two to reveal the terminals with the attached wiring.

When the wiring is visible, you can make notes regarding the placement of the wires.

After the wiring pattern is recorded, it is time to start the removal process for the old thermostat. Turn off the power to your heating and cooling system. Loosen each of the screws holding the wires in place. Remove the screws that go through the thermostat and into the wall. This should allow your thermostat to drop loose from the wall.

Carefully remove the wires from the screws.

Pull them gently through the body of the thermostat. Care is needed because these are very small wires and can be broken easily. Once all of the wires are removed, set the old thermostat aside.

Read through the directions for the new thermostat.

You need to be familiar with the recommended installation instructions from the manufacturer. Sometimes there are cautions or variations listed for the specific unit that you are installing. Generally, the changes are minor and will not vary significantly from the normal installation process. If possible, review the installation instructions for your heating and air conditioning control.

Thread the wires through the ports in the body of the new thermostat.

Place the ends of the wires around the proper screws. Tighten the screws to secure the wires. If this is too difficult with the thermostat loose, fasten it to the wall with the wires passed through the body and then finish the connections once the thermostat is secure.

Place the cover onto the thermostat.

Snap the cover into position. Do any necessary programming to make the unit function properly. Turn on the power to the heating and air conditioning system. Set the desired temperature on the thermostat. The system should begin to cycle so that the ambient temperature will be increased or decreased to meet the conditions that you have set.

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