How to Replace a Two-Wire Thermostat with a Digital Thermostat

Home and Garden

In this article, we will guide you through the process of replacing a traditional two-wire thermostat with a more advanced digital thermostat. Upgrading to a digital thermostat offers several benefits such as increased accuracy, programmable temperature settings, and energy-saving features. Before you begin, make sure to turn off the power to your heating and cooling system.

1. Gather the Necessary Tools

Before starting the replacement process, ensure that you have the following tools:

  • Screwdriver (flathead and Phillips)
  • Wire strippers
  • Electrical tape
  • Drill (if necessary)

2. Identify the Wiring

The first step is to identify the wiring of your existing two-wire thermostat. Take note of the color and terminal connections for each wire. Typically, the two wires are labeled “R” and “W” for heating systems. However, it is essential to refer to the wiring diagram provided with your specific thermostat model for accurate identification.

Two 2 wire Honeywell digital thermostat to replace mercury switch. Convert from mercury switch

2-Wire Installation for Honeywell Thermostat

3. Turn Off the Power

Before handling any electrical connections, ensure that the power to your heating and cooling system is turned off. Locate the circuit breaker or fuse box and switch off the corresponding circuit.

4. Remove the Old Thermostat

Use a screwdriver to remove the old thermostat from the wall. Carefully disconnect the wires from the terminals, ensuring not to let them fall back into the wall. If necessary, use electrical tape to secure the wires and prevent them from slipping away.

5. Prepare the New Thermostat

Read the instructions provided with your new digital thermostat carefully. Some models may require additional setup steps before installation. Ensure that the batteries (if applicable) are inserted correctly or that the thermostat is connected to a power source.

6. Mount the New Thermostat

Align the mounting plate of the new thermostat with the existing holes in the wall. Use screws and a screwdriver to secure the plate in place. Make sure it is level and firmly attached.

7. Connect the Wires

Following the wiring diagram provided with your new thermostat, connect the wires to the corresponding terminals on the thermostat. Most digital thermostats have clear labels for each wire connection. Use wire strippers to remove a small portion of the wire insulation and ensure a clean connection. Tighten the terminal screws to secure the wires in place.

8. Attach the Thermostat Cover

Once the wires are connected, carefully snap the thermostat cover onto the mounting plate. Ensure that it is firmly in place and aligned correctly.

9. Restore Power

Go back to the circuit breaker or fuse box and switch on the circuit corresponding to your heating and cooling system. The power should now be restored.

10. Set Up and Program the Digital Thermostat

Now that the new thermostat is installed, refer to the manufacturer’s instructions for setting up and programming the digital thermostat. Most models have an intuitive user interface that allows you to adjust the temperature, set schedules, and customize preferences.


Replacing a two-wire thermostat with a digital thermostat is a relatively straightforward process. By following the steps outlined in this article and carefully reading the instructions provided with your specific thermostat model, you can enjoy the benefits of enhanced temperature control and energy efficiency.

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