How to fix Nest E80 error

It is winter and your Nest Thermostat is acting up when you turn the heat on. It gives you an E80 error code instead leaving you frustrated and in the cold. Instead of sitting in the cold, you can troubleshoot your system’s wiring in a few steps.

There are two main types of error codes on a Nest thermostat; E and N errors. The N errors aren’t that critical since they only affect some features of your thermostat. E errors on the other hand are critical as they won’t allow you to control your cooling and heating until they’re fixed.

You’ll see an E80 error code with a message ‘No power to Y1 wire’ when your Nest Thermostat detects that the Y1 wire in your system has stopped working because:

  • Your AC’s safety cut-out switch has tripped, preventing your AC from turning on in extremely cold weather or
  • Your HVAC system is in need of maintenance.

You can resolve the Nest E80 error by installing a common wire (C-wire) or carrying out maintenance on your system.  

A summary of E80 error causes and how to fix

How to fix
Nest E80 error showing
Your Y1 wire in your HVAC system has stopped working due to lack of maintenance or your AC’s safety device has been activated in extremely cold weather conditions.
Connect a common wire (C-wire) to your Nest Thermostat to ensure constant power supply from your AC to your Nest Thermostat’s internal battery.


Get a professional to carry out maintenance on your HVAC system.


Consult your local professional to fix it for you.

What are the causes of E80 error?

Your Nest Thermostat charges its battery using your system’s heating and cooling wires (Y1) and can work without a common wire. The work of a C-wire is to ensure constant supply of power to your Nest Thermostat’s internal battery.

The Y1 wire in heat pump systems controls the compressor that then heats and cools your home while in conventional cooling systems, the Y1 controls the first stage of cooling.

When power from your AC stops flowing to your thermostat, you’ll get this error. There are several reasons for your AC not sending power to the thermostat. They include:

  1. Your HVAC system is in need of maintenance. With the help of a HVAC professional, you can find out if you need system maintenance.
  1.  If you live in an area with cold temperatures in winter it may damage your air conditioner. You AC come with a safety cut-out switch that automatically turns off in extremely cold weather to prevent damage to the AC. This stops the flow of power from the AC to the thermostat.

How to fix


  1. From the breaker box/fuse box, turn off your system’s power to avoid any electrical accidents.
  2. Remove the thermostat display off the base by gently pulling it.
  3. Take a photo of the thermostat’s wiring for future reference.
  4. From the thermostat’s base, remove any Y wires (Y, Y1, and Y2). Remove the Rc wire in case you have both the Rh and Rc wires.
  5. Use electrical tape to mask the exposed end of each wire you removed.
  6. Clean all the wires using a sharp object like a pocket knife and push them all the way in their respective connectors.
  7. Ensure the wires behind are all pressed down in their respective connectors before reattaching to prevent the display from not seating in properly.
  8. Press the display onto the base until you hear a click to confirm it’s properly seated.
  9. Turn power back on to your system and after the Nest thermostat turns on, check to confirm if the error is gone.
  10. If the E80 error code is not showing, then you can turn on the heat. If your thermostat is not starting up:

Use a USB to connect to its USB port on the display’s back and charge for 5-10 minutes or until it turns on and put the display back on the back by pressing it until it clicks. Try turning on the heat.

11. If the error is still showing, connect the common wire. Make sure to turn off power to your system from the breaker box/fuse box.

At the back of the base in the wall, look for a wire labeled ‘C’ and push it into the connector labeled ‘C’. If you can’t see your C-wire, look out for an unused wire in the wall. If you see ‘The wiring to your equipment has changed’, select ‘continue’ until you’re done.

12. Turn power back on to your system and after the Nest thermostat turns on, check to confirm if the error is gone.

NB: Though you’ve gotten your system back up, it is recommended to consult a professional to come and take a look at your system and ensure its all has been properly fixed.

It is important to note that your Nest Thermostat requires a voltage of 3.6V for the display to turn on and if all is well, the voltage should generally be more than 3.6V. Also, for your thermostat to perform a software update, your battery should have a 3.7V.

Before working with any wires, you SHOULD always turn off power to your system from the breaker/fuse box to avoid any electrical-related accidents.


Constant power supply is required for your Nest Thermostat to work optimally. Although a common wire is not really needed during installation for your thermostat to work, it is good to connect it to just future power inconveniences.


Why is my Nest Thermostat cooling delayed?

Your system may have a built-in delay which is normal and helps prevent excessive wear and tear on your system and takes just a few minutes.

What is the work of the Y2 wire?

The Y2 wire is used to control your compressor’s second stage to allow different levels of heating and cooling in a heat pump. In a conventional cooling system, it helps cool the home faster by controlling the second stage of cooling.

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