You can replace a thermostat without an electrician.
A thermostat for your furnace or furnace and AC are pretty easy to replace and the are low voltage.
Before replacing the thermostat you should mark the wires so you can tell which wire is which.
The new thermostat should also have a wiring diagram which is pretty easy to follow.
If you're unsure on how to replace the thermostat then a handyman could replace the thermostat or an HVAC company could also replace the thermostat for you.
If your thermostat controls your heat, you will have a white wire.
The Y wire is yellow and connects to your air conditioning compressor.
The G wire is green and connects to the fan.
Rc and Rh: The red wire(s) are the power source for your thermostat.
A typical eight-wire thermostat will have the following wire configuration: red wire to "R" terminal, white wire to "W" terminal, green wire to "G" terminal, yellow wire to "Y" terminal, black wire to "C" terminal, blue wire to "Y2" terminal, brown wire to "W2" terminal, and orange wire to "Aux" terminal.
Red or hot wire for 24V powers the thermostat continuously, linking to the R terminal.
Blue wire or common wire for 24V to complete the circuit linking to the C terminal.
A white wire connecting to the heating unit linking to the W terminal.
A green wire connecting to the fan linking to the G terminal.
While your thermostat may not technically need a C-wire to operate, it gets the power for its screen and Wi-Fi capabilities through “phantom power” or “power stealing.” Basically, this means your thermostat gets a kick of extra power whenever your HVAC system is running.
The most common thermostat cabling is 18/5 (18 gauge, 5 conductor), because 5 conductors typically offer enough functions for a modern thermostat/low voltage device.
Some older thermostats do indeed have three connections: 2 for switching and one (neutral feed)to power a heating resistor to act as an "anticipator".
However if you are using two 2-port motorized valves, then you need the third wire to isolate the valves from each other.
What if I have an O and B wire thermostat?
O, B, O/B: These wires are responsible for switching the changeover valve in a heat pump system.
The O wire reverses the valve from heating to cooling, and the B wire switches the valve from cooling to heating.
Sometimes it might be a single O/B wire instead of two separate wires.
There is no standard for the color of the RH wire, but most units use a red one.
The RC wire, on the other hand, refers to “red cooling”.
It's the same with the RH wire in that it powers the thermostat.
If there are no yellow wires, it is probably because the manufacturer has chosen to color this wire blue instead.
If you know that your system has two stages of cooling, but there is only one yellow wire, it's also possible that the second wire is colored light blue.
If you have two wires, R or RH go into the R terminal and RC into the RC terminal.
If you have more than one wire (for example, you have a wire labeled R and another wire labeled Rc), remove any jumpers between the R and Rc terminals or push the switch to open the RC terminal to insert a wire.