How to Wire a Heater Thermostat

A heater thermostat can help save you money by limiting the amount of energy used in your home. Most modern heaters will come with a thermostat already fitted by the manufacturer. If you want to upgrade your heater, or if you want to replace a broken thermostat, you may find that wiring the thermostat is the most complicated part of the process. The following steps will guide you through the job of wiring your heater thermostat.

Step 1 - Know Your Heater Thermostat

Different thermostats will require different levels of wiring. You should also identify your model of heater; models can also vary in the number of wires they extend. Check that your heater and the thermostat are compatible. If they do not match, you should not install the thermostat under any circumstances, as you could be creating a fire hazard.

Step 2 - Turn Off the Power

Before you go any further, you should ensure that the mains power supply is turned off at the outside switch.

Step 3 - Access the Wires 

Remove your old thermostat. Take off the wall plate by unscrewing it from the wall. This plate usually conceals the wires you need. Use the pliers to cut down any damaged or broken wires.

Step 4 - Install the Wires

If you have read the instructions which came with your heater thermostat, you should know where these wires go. Remove the side of the heater and connect the wires into the strain relief connector, which will be noted on the instruction manual which came with your heater. Leave a foot or so of wire for connection to the thermostat. Turn the heater upside down and ensure that the wires coming from the heater are fully connected inside, particularly on the grounding pigtail connector. Pull any excess wire length away from the heater and through the hole in the wall.

Step 5 - Connect the Heater Thermostat

Heater thermostats will come with a series of letters inscribed down the sides of their wire terminals, small holes each filled by a tiny screw. Each of these letters corresponds to a color of wire coming from the heater. For example, "R" or "RC" terminals connect to the red wire.

Unscrew your terminal but take care not to fully remove the screw. Then proceed to push the wire through the hole you created and tighten the tiny screw so it holds the wires in place. You may need to remove the insulation around each wire. If so, use either pliers or a wire cutter, but don't take back too much insulation. Take care to avoid bare wires touching when they are connected to terminals.