Home Improvements

How To Replace Your HVAC Thermostat

A fault thermostat impacts the efficiency of your HVAC system. Therefore, you should make sure that the thermostat is fine and if it goes bad, hire an air conditioning repair service for replacement. If you’re a DIYer, learn how to replace the thermostats of your HVAC system.

AC Thermostat Installation Guide

When To Replace Your HVAC Thermostat?

  • AC not turning on: If your AC is not turning on and you have checked the power to the AC and it’s fine, then the thermostat may be faulty and require a replacement.
  • Faulty temperature readings: Malfunctioning thermostats show faulty temperature readings making your AC overwork or turn off before the completion of its cycle.
  • Display not working: if you have a thermostat with a display and its display has stopped working, the thermostat is faulty.

Before going ahead with the replacement, change the batteries of the thermostat to check if the drained batteries were causing the problem. If the problem persists, then follow the below step-by-step thermostat replacement guide.

Choose A Thermostat

There are different types of thermostats and all don’t work with all kinds of HVAC systems.

Manual Thermostats

This is the basic form of a thermostat that only has buttons that can you press to set temperatures or a dial.

Digital Non-Programmable Thermostats

A digital non-programmable thermostat has an LCD for seeing the settings and changing them as required. You can’t schedule different temperatures for different times of the day with these because they are digital but non-programmable.

Programmable Thermostats

Programmable thermostats are energy efficient because you can set them to change the temperatures automatically during different times of the day.

Smart Thermostats

Smart thermostats also have the capabilities of programmable thermostats. However, they have other features as well like they can be controlled from your mobile phone. They are connected to Wi-Fi so you can turn on the AC, change the temperatures, or shut it down from anywhere. You only need to be connected to the internet.

Considering Your HVAC System For Choosing A Thermostat

Most thermostats work on the common heating and cooling system, but you should be sure that the thermostat you’re selecting will work with your HVAC system. You should note the brand and model number of your AC and the thermostat and show it to the salesperson and ask them if the thermostat you’re buying will work with that.

You can also have an HVAC technician visit your home and check the HVAC system and thermostat to let you know which thermostats are fine for your unit.

Replacing A Non-Programmable Thermostat

If you have selected a non-programmable thermostat, use these steps to replace and install a new thermostat.

Turn Off The HVAC System

Go to the breaker panel usually in the garage of a home and turn off power to your HVAC system to prevent any accidents.

Remove The Old Thermostat

Hold the upper part of the old thermostat and slide to one side or push it to your side for separating it from its mount. If you find some screws, unscrew them first before removing the upper part of mounting plate of the old thermostat.

When wires are exposed, don’t remove them and take a picture of the wires’ connections. This will help you connect wires to the new thermostat. After noting the connections, use a thermostat screwdriver to disconnect the wires from the old thermostat mount one by one. When you remove a wire, label it accordingly.

Install The New Thermostat

The new thermostat will have two parts as well. The mounting plate and the thermostat. Remove the old thermostat’s mounting plate and use a screwdriver to install the new mounting plate.

Connect the wires to each terminal similar to how the old thermostat was wired. Use the pictures you took of the old wiring for help. You should also refer to the instructions that came with your thermostat inside the packaging.

Tighten each wire with a screwdriver, but make sure not to overtighten it because it can damage the wire. If the wires are large in length or corroded, you should cut the corroded parts, strip the wires, then connect the new, stripped parts of the wires to their respective terminals.

After finishing up with the wiring, all you need to do is place the thermostat on the mounting plate. Power on the AC. Check your thermostat’s instructions to learn if it requires batteries or if it will take power from the wiring. Non-programmable thermostats don’t require continuous power from the wires, they typically need batteries. Check which batteries are required and insert the batteries for the thermostat to work. If the thermostat doesn’t work, call in HVAC repair services Fairfax.

Installing A Programmable Thermostat

Power Off The HVAC System

To avoid an electric shock, make sure to power off your AC from the circuit breaker before beginning to replace the thermostat. After this, remove the old thermostat by sliding or pulling it to expose the wires and the wall plate of the thermostat. Use a voltage tester to touch the voltage and verify that there is no power. If you detect power, you may need to turn off power to the whole house.

Label The Wires And Remove The Plate

You will see a few wires coming out from the wall connected to the wall plate. Label the wires with masking tape and take photos so you know the connection point for each wire. Make sure the wires don’t touch each other. Bend the wires after labeling them.

Use a screwdriver to remove the screws of the mounting plate or base and remove the base. Moreover, take out the plastic screw anchors as well if you see them.

You can also spray a small amount of non-expanding insulating foam in the space between the wires for a more accurate thermostat reading.

Install The New Thermostat

Take the base of the new thermostat and place it where the old base was. Use a torpedo level to make sure it’s level. You can mark the area or begin tightening the screws of the base directly if plastic screw anchors are not needed. However, if they are required, use a drill machine for making holes for the plastic screw anchors and insert them into the drilled holes. Place the thermostat base on the anchors and tighten its screws.

For connecting the wires, use the labels you created and photos taken in the previous step. Moreover, read the user manual of the thermostat as well. Make sure to tighten the wires after connecting them to their terminals.

After this, put batteries in the base if there is a compartment for them. If there isn’t, your thermostat will use power from the wires. Moreover, many thermostats that use your home’s power for working still require batteries in case of a power outage.

When done, put the cover of the thermostat on the base and turn on your air conditioning system. Check your thermostat and if it doesn’t run or show problems, you should consult an expert.


Your HVAC system’s thermostat regulates the temperature inside your home so you must replace it if it shows problems like faulty temperature readings, not responding, AC not turning on, and others. Use the above steps for replacing both non-programmable and programmable thermostats. If you’re not sure of the cause of the AC problems, consult air conditioning companies Vienna.

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