This is a guide to replacing a thermostat

Before You Start

Tools You’ll Need

• Small flathead and Phillips screwdriver

• Phone camera (for wire photos)

• Drill (only if the new base plate uses different holes)

• Level (optional but helps the thermostat look straight)

Safety First

Turn off power to your HVAC system at the breaker.

This prevents the low-voltage wiring from shorting and protects your equipment.

1. Remove the Old Thermostat Cover

Most snap off with a gentle pull from the bottom or sides.

If it’s a very old style, there might be a small screw holding it on.

2. Take a Clear Photo of All Wiring

This is one of the most important steps:

Make sure the photo shows:

• Labels on each wire

• The terminal letters the wires connect to (R, Y, G, W, C, etc.)

This will save you if anything gets confusing later.

3. Label the Wires (If Your New Thermostat Includes Stickers)

If your new thermostat kit came with wire stickers, tag each wire.

You can also use small pieces of tape and write the letters if needed.

4. Unscrew the Wires & Remove the Old Base

Loosen the small terminal screws and gently pull the wires out.

Unscrew the baseplate from the wall.

Tip:

Don’t let the wires fall back inside the wall.

Wrap them around a pencil or tape them to the wall so they stay accessible.

5. Install the New Thermostat Base

Hold the base against the wall and level it if you want it perfectly straight.

Then:

• Mark new screw locations if needed

• Install wall anchors if the holes don’t line up

• Screw the new base tightly to the wall

Run the wires through the center hole.

6. Connect the Wires to the New Thermostat

Match wires by letter, not color.

Your earlier photo helps here.

Typical connections:

• R → Power

• Y → Cooling

• G → Fan

• W → Heat

• C → Common (only for WiFi thermostats)

Tighten each terminal screw snugly.

7. Attach the Thermostat to the Base

Most modern thermostats snap or slide on.

Make sure it fits securely and sits level.

8. Turn Power Back On

Go back to the breaker and restore power.

The thermostat should power up within a few seconds.

If it doesn’t, check:

• The C wire (if your model requires it)

• Whether the R wire is firmly connected

• Whether the thermostat is fully seated on the base

9. Program & Test the System

Set your desired heat/cool temperature and make sure:

• The outdoor unit kicks on for cooling

• The furnace or heat strips activate for heating

• The fan runs correctly

Test each mode to confirm everything works.

❗ Common Mistakes to Avoid

• Forgetting to turn the power off

• Misconnecting the R/RC/RH wires

• Installing a WiFi thermostat without a C wire

• Letting the low-voltage wires slip into the wall

• Mounting the thermostat crooked or too close to a heat source (lamp, sunlight)

Find the tools and thermostats you need here!