Okay, this sounds like a common but potentially tricky situation. Let's break it down and figure out how to re-install this thermostat safely and effectively.

Understanding the System Gas Radiant Heater with 2-Wire Connection

This likely controls a gas valve inside the heater. When the thermostat calls for heat, it closes the circuit, energizing the valve and allowing gas to flow.

120V Supply

You have 120V available from the MC cable.

120V to 24V Transformer

This transformer is essential. Thermostats often operate on low voltage (24V AC) for control. It powers the thermostat itself and the signaling circuit.

Single Pole Switch

This switch likely controls the power to the 120V to 24V transformer.

Wiring Diagram and Steps

Here's how the system should be wired. IMPORTANT

Before doing ANY wiring, ensure the circuit breaker for the 120V supply is OFF and locked out to prevent electrocution. Verify power is off with a non-contact voltage tester.1.

Power Supply (120V)

The MC cable should provide the 120V power. Connect the black (hot) wire from the MC cable to one side of the Single Pole Switch. Connect the other side of the Single Pole Switch to the primary (120V) side of the transformer. Connect the white (neutral) wire from the MC cable to the other connection on the primary (120V) side of the transformer. Connect the green (ground) wire from the MC cable to the metal enclosure of the transformer and/or any grounding points in the box.2.

Transformer Secondary (24V)



R (Red) Terminal

Connect one wire from the 24V secondary side of the transformer to the "R" terminal on the thermostat. This is your 24V power supply to the thermostat.

W (White) Terminal

Connect the other wire from the 24V secondary side of the transformer to one of the wires coming from the gas radiant heater. Connect the other wire coming from the gas radiant heater to the "W" terminal on the thermostat. This completes the circuit to the gas valve when the thermostat calls for heat.

Important Considerations and Troubleshooting Safety First

Turn off the power at the breaker BEFORE doing any wiring. Double-check with a non-contact voltage tester.

Thermostat Compatibility

Make sure the thermostat you're using is compatible with a simple 24V, 2-wire heating system. Many modern thermostats require a "C" wire (common wire) which this system appears not to have. If it needs a "C" wire, you'll need to investigate further.

Wiring Diagram on Thermostat

Most thermostats have a wiring diagram printed on the back or in the instructions. Refer to that diagram for confirmation.

Polarity on 24V Doesn't Usually Matter

With AC voltage (like 24V AC), the polarity of the wires doesn't typically matter. However, it's good practice to maintain consistency.

"C" Wire Issues

If the thermostat needs a "C" wire and you don't have one, you'll need to investigate further. Some options include:

Adding a "C" Wire

This is the best solution, but may involve running new wiring from the furnace/heater to the thermostat.

Using a "C-Wire Adapter"

These adapters can sometimes "borrow" a "C" wire from the existing wires, but they don't always work reliably.

Testing1. Turn on the Breaker

Once you've double-checked all wiring, turn the circuit breaker back on.2.

Turn on the Switch

Make sure the single pole switch is turned ON.3.

Thermostat Operation

Set the thermostat to call for heat. You should hear the gas valve open in the radiant heater, and the heater should start warming up.4.

Thermostat Off

Set the thermostat to a temperature below the room temperature. The gas valve should close, and the heater should stop.

If it Doesn't Work Voltage Check

Use a multimeter to verify you have 120V at the primary side of the transformer when the switch is ON, and 24V AC at the secondary side.

Thermostat Settings

Make sure the thermostat is properly configured for a 2-wire heating system.

Gas Valve

If the thermostat seems to be working, but the gas valve isn't opening, there may be a problem with the valve itself.*

Transformer Issues

a short in the system may cause the transformer to burn out. Check that the transformer has the proper voltage output.

Disclaimer: I am an AI chatbot and cannot provide professional electrical advice. This information is for general guidance only. Working with electricity can be dangerous. If you are not comfortable performing these tasks, hire a qualified electrician. It's essential to comply with all local electrical codes and regulations. Flag for review