Troubleshoot a "No power" alert on the Nest Thermostat

If your Google Nest Thermostat is not receiving power from your heating, ventilation, and air conditioning (HVAC) system, it will tell you there’s a problem. There are a few things you may notice on your thermostat:

  • A “No power” or “No system power” alert will appear.
  • A help code should also appear. For example, if appears, E298 is the code you need to troubleshoot.
    • N help codes can be dismissed, but they may appear again if the problem persists.
    • E help codes can’t be dismissed, so they won’t disappear until the issue is fixed.
  • The Settings Nest Thermostat Settings alert icon will also have an exclamation point. If you hover over it, it will say ”Equipment error.”
  • A “low battery” or “very low battery” alert may appear if the backup batteries continue to lose charge.
  • Your thermostat may disconnect from Wi-Fi if it’s not receiving power, even if the battery level is good.

A “No power” alert can be caused by the following:

  • The thermostat wiring is incorrect.
  • The HVAC system is powered off at the circuit breaker, fuse box, or system switch, or there’s a power cut.
  • The HVAC system is experiencing some other issue that prevents it from sending power to the thermostat wires.

Here are some steps to troubleshoot a “No power” alert on your thermostat.

This article only applies to the Nest Thermostat.

Nest Thermostat 3/4ths view

How to tell which thermostat you have

Note: If your Nest Thermostat won’t turn on, or if your Nest Thermostat E or Nest Learning Thermostat is having power issues, go to our Troubleshoot when your Nest thermostat won’t turn on article.

Before you troubleshoot

  • If your thermostat shows a low battery alert, change the batteries first so that you can control your system and stay comfortable while you troubleshoot.
  • If you see a help code (like E294, E298, or M20), follow instructions in our Troubleshoot Nest thermostat help codes article to see if that resolves the issue.
  • If you recently turned power off at the circuit breaker of the heating and cooling system, make sure it’s back on.


1. Go to equipment information

To narrow down possible causes of a “No power” alert, use your thermostat to navigate to its equipment information.

  1. If needed, tap the touch bar to wake up your thermostat. Tap again to open the Menu view.
  2. Slide on the touch bar to hover over Equipment Nest Thermostat equipment.
    • A “No power” or “No system power” alert will appear.
    • An Error code (such as E## or N##) should also appear.
  3. Tap the touch bar to select EquipmentNest Thermostat equipment.

2. Check the wiring

On the equipment screen, check for wires that appear as grey. This means that the wire is not sending voltage to your thermostat. Some wires, like a C or R wire, need to send voltage to keep your thermostat powered on.

If all the wires are grey, the system may be powered off or experiencing some other power-related issue. Check that the system is powered on at the circuit breaker, fuse box, or system switch.

If any wire is grey, it isn’t electrically detected by your thermostat. If you incorrectly entered a wire in the app and your system doesn’t have that wire, it will appear as grey too. Follow the steps below to check that each wire is properly connected.

Important: You must turn the system off before checking the system wires. This will help prevent damage to them and your thermostat.

  1. Turn power off for the system. The power switch will usually be in the circuit breaker, fuse box, or system switch. In some homes, it will look like a light switch near the heating or cooling equipment.
    Note: There may be one switch for heating and one for cooling, or a single switch for both.
  2. Pull your thermostat away from its base to remove it.
  3. To disconnect each wire, push down its connector tab and gently pull out the wire. Then, do the following as needed:
    • Straighten the wire end.
    • Strip the wire to expose ⅓" to ½" of copper.
    • Seat the wire fully into the right connector.
  4. After all the wires are connected, re-attach your thermostat to its base.
  5. Turn the power for the system back on.
  6. After a few moments, use your thermostat to go to the Menu view and then Equipment Nest Thermostat equipment, then check if the issue is resolved.

3. Contact a local pro

If you think wires are incorrectly connected to your thermostat and want additional help, contact Nest support. You can also read more steps to troubleshoot Nest thermostat help codes.

If you think there may be a problem with the heating and cooling system (for example, your thermostat recommends a C wire), contact a local pro to diagnose and service your system.

Was this helpful?
How can we improve it?