If your heating system has only two wires, the job of the thermostat is simple. All it has to do is turn the heat or the cooling on and off. Theres also no thermostat blue wire, or common wire, to power the thermostat, so it has to operate on its own, either using batteries or mechanical temperature detection.

Can I use a 2 wire thermostat on a 4 wire system?

Replacing an outdated four-wire thermostat with a newer model that uses two wires is not complicated, once you purchase the thermostat from a home-and-garden shop or hardware store. The procedure to install the new thermostat is straightforward and does not require the assistance of a certified electrician.

Why did my thermostat catch fire?

The safety commission reports that contact between the thermostat wires and household line voltage can damage the thermostat and cause a fire.