How to Replace an 8 Wire Thermostat

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Things You'll Need

  • Screwdriver

  • Drywall anchors

  • Screws

  • Labels

  • Cordless drill

  • Wire stripper

If you've ever pulled off your thermostat, you'll notice that there are a number of wires attached to it. These wires run to the furnace and communicate with it. Each wire controls a specific function on the thermostat. When it becomes necessary to replace your thermostat, you'll have to make sure each wire is connected to the correct terminal on the thermostat so that your furnace functions properly. It may look challenging, but to replace an eight-wire thermostat, all you need are a few tools.


Step 1

Turn off the power to the furnace. Either turn off the switch by the furnace or turn off the circuit breaker in the circuit breaker panel.

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Step 2

Pull the thermostat off of its wall plate with gentle pressure. Be careful not to damage the wires by pulling too hard.

Step 3

Disconnect all eight thermostat wires one by one. Label each one as you disconnect it according to which lettered terminal it was connected to. They are typically fastened to the thermostat with a set screw, so simply loosening that up should free them.

Step 4

Remove the old wall plate from the wall and discard. Attach the new wall plate to the wall. Use drywall anchors and screws to secure it to the drywall.


Step 5

Reattach each thermostat wire to the new thermostat. Take off the label after you connect the wire to its corresponding terminal.

Step 6

Attach the thermostat to the wall plate by pushing it on with gentle pressure. Make sure none of the thermostat wires get pinched as you push it on.


Step 7

Turn the power back on to the furnace and carefully read the instruction manual for the new thermostat. Set the temperature to your desired setting. Set up the programs if it is a programmable 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. However, please note the color configuration may vary depending on who installed the system.


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