Take a picture of the 3 wires. Note the color – red, white, and green – and the terminals – R, W or W1, G.

HVAC technicians know the color-coding by heart; they can just remove any Honeywell thermostat, replace it with the new one and reconnect the terminals.

Knowing how to wire a 3-wire thermostat is fairly easy compared to 4 and 5-wire thermostats: 4 Wire Thermostat Wiring (Heat Pumps, HVAC) Referring to your photo, remove and label each wire. If a terminal has multiple designations like W and O/B, it will be labeled as W and O/B and not just one or the other. All combination boilers should have a room thermostat fitted. Without one, there will be no way for the air temperature to be controlled. Volt free terminals Most thermostats do not require an earth connection, however an earth should still be provided at the thermostat position. The usual method is to provide 3 core and earth cable between the boiler and thermostat. This will allow either a 2 wire or 3 wire thermostat to be fitted. In recent years, thermostats have become more and more high-tech. There are now several different types of thermostats on the market, from the standard programmable thermostat to the more advanced Wi-Fi thermostat. If you’re looking for a high-tech thermostat that is easy to use and doesn’t require any programming, then a 2-wire smart thermostat may be the perfect option for you.

Spreading them apart will create at least a 2×2 inch crosssection, and the wires will be suspending on the wall (instead of on the thermostat). Overall, the Nest thermostat is a very smart and useful gadget that allows you to keep an eye on your home’s temperature at any given moment. 2. Ecobee Smart Thermostat (5th Gen) O” or the orange thermostat wire is for reverse valve cooling. Most bigger heat pump manufacturers like Trane, Goodman, Lennox, and so on have the orange wire that goes to the condenser (located in the outdoor unit of heat pumps). Do keep in mind that with so many different thermostats, each wire code can have a different color wire. “O” wire, for example, is not necessarily always orange. If a technician that installed your thermostat used a different color, you might have a problem reconnecting the wires. That’s why this next section is so important: Removing The Old Thermostat (Take Photo)An important note: Keep in mind that dealing with electrical circuits can be harmful to yourself. That’s why always follow the appropriate safety measures when working on live electrical circuits. For more information about the wires and their ampacity, consult the AWG gauge chart with wire sizes for specific amps here. If you are DIY thermostat wiring, here’s the easiest thing to do before removing the old thermostat: If you’re planning to replace the old thermostat, don’t immediately remove the old thermostat. First of all, make sure you will be able to correctly wire the new thermostat. If you unscrew the terminals and remove the wires right away, you may have problems reconnecting the wires to the new terminal. Make sure you have a picture of how the wiring to the old thermostat looks like before continuing. Make Sure To Spead The Wires (You Don’t Want To Lose Them In The Wall)