Troubleshoot Nest thermostat help codes

You might see a help message on your Google Nest thermostat or in the app if there’s a problem detected with the thermostat’s wiring or internet connection. 

 

When this happens, the message will end with a link, such as "nest.com/e297" or "g.co/nest/needWY". The code you need or the wire that needs your attention is at the end of the link.

Winter helpful troubleshooting

If your Nest thermostat shows an E10, E30, E66, E80, E116, E160, E196, or M13 error during very cold weather, visit g.co/nest/winterhelp to learn how fix it.

 

Use the interactive troubleshooting guide or follow the instructions in the article below.

Click here for the interactive troubleshooting guide

For general troubleshooting, select the section with the letter of your help code below, and follow the instructions for your code.

T error codes

You may see one of these help messages while running a System Test after you install your thermostat. The code you see will tell you which part of your system had an issue during the test. 

T01 - single stage fan problem T02 - single stage cooling problem T03 - two stage cooling problem T04 - forced air system problem T05 - radiant heating problem T06 - radiator heating problem

T07 - baseboard electric heating problem T08 - humidifier problem T09 - dehumidifier problem T11 - two stage fan problem T12 - three stage fan problem

Troubleshooting steps for each help code are very similar even though the reasons for the code can vary.

Note: There are specific troubleshooting steps for certain errors in some steps.

1. Run the test longer 

• The System Test will run for 35 minutes before it stops automatically.
  • Select Keep Testing on your thermostat if needed or restart the test by going to Settings Equipment on your thermostat.
  • Select Continue    Test.
• Many systems have a built-in delay so it might be 5 minutes or more before your system turns on.
• If you’re testing a radiant system, electric baseboard heating, or a system with radiators it typically takes a while before you can feel the floor baseboard or radiators getting warm. Try waiting up to 30 minutes to see if they warm up.

2. Make sure your system has power 

• Check that the breaker switch or fuse that controls power to your system is set to on. System power should be turned off during thermostat installation to help prevent blowing a fuse but it should be turned on for testing.
• Also check the switches for other system components such as fans.  They may have a separate switch which also needs to be set to on.

3. Check that your thermostat is wired correctly

Important: Protect yourself, your thermostat and your system. Turn off power to your system and thermostat at the breaker or fuse box before exposing or adjusting any wiring.

1. Pull off the thermostat display.
2. Check that the wires are inserted correctly in the thermostat.

   Check that each wire is fully inserted into its connector and that every connector with a wire is down as shown. Check that each wire has ⅜ inch (6mm) of exposed wire.

3. Put the display back on the base and turn the power to your system back on.
4. Check to see if your thermostat is working. If it still doesn’t work, check that your system wires are connected to the right connectors. Use the wiring diagram the app gave you during setup to move the wires to the right connectors.
   • Turn off power to your system and thermostat at the breaker or fuse box.
   • If you don’t have the wiring diagram, refer to the picture of your thermostat wires that you took when it was installed. If you didn’t take a picture or can’t find it, follow these instructions to access your system’s control board and take a picture of the wires. Use this picture to enter the wires into the app.

     In the Nest app

     1. Open the Nest app.
     2. Use these steps to add the thermostat to the app to get the wiring diagram.
        • If you don’t have other products in the app
          • Tap Add product on the home screen and follow the app instructions. 
        • If you have other products in the Nest app 
          • Tap Settings  in the top right. 
     3. Select Add product.
     4. Follow the app instructions. Make sure you choose the Start installation even though you’ve already installed your thermostat.
     5. Follow the app instructions until the app asks you to enter your thermostat wires. Use the picture you took of your old thermostat’s wires or your control board wires as a reference.
     6. The app will give you a wiring diagram. Move the wires to the right connectors to match the wiring diagram. If you need to move wires, your thermostat may ask you a few questions.
        • Important: Make sure the wires have ⅓ to ½ inch (6mm) of copper exposed and that the wire connectors stay all the way down.
     7. After you have the wiring diagram, you can exit device setup.

     In the Home app

     1. Open the Home app.
     2. Tap Add + at the top left of the home screen.
     3. Tap Set up device and follow the app instructions until you get to the wiring step. 
        • Use the picture of your old thermostat’s wiring to enter the wires into the app.
        • After you have the wiring diagram, you can exit device setup. 
     4. Move the wires to the right connectors to match the wiring diagram.
        • Make sure the wires have ⅓ to ½ inch (6mm) of copper exposed, the wire is fully inserted into the connector, and that the wire connector button stays down.
     5. Replace the thermostat display and turn your system power back on.
5. Turn power to your system back on at the breaker or fuse box.

6. Re-test your system. On your thermostat go to Settings > Equipment. Then select Continue > Test.

If you’ve completed all the troubleshooting steps above and your thermostat still isn’t working correctly, contact a local pro for more help.

4. Steps for specific system types 

If you have one of the codes in this table, check your system for the issue listed below then restart the System Test if needed. 

If you're not sure which type of system you have, you can check here.

Help code	Troubleshooting
T06 error Your system has radiators	Check that the radiator valves are fully open so that hot water can circulate to the radiators.
T07 error You have an electric baseboard system	Most baseboard systems are high voltage (120 V) and are incompatible with Nest thermostats. 24V baseboard systems are much less common so double check your system voltage. If it’s 120 V disconnect the Nest thermostat and reinstall your old one.
You have a heat pump	If there’s a wire (usually orange) in your thermostat’s O|B or * O|B connector you have a heat pump. Heat pump systems can heat when they’re supposed to cool (or cool when they’re supposed to heat) if the O|B wire isn’t configured right during thermostat setup. See this article for specific steps to change the setting.
T09 or T08 error You have a dehumidifier or humidifier	We strongly recommend professional installation for systems with dehumidifiers or humidifiers because of setup complexity. Nest thermostats have one connector ( * or * O|B) for dehumidifiers or humidifiers. But these components often have two wires so a relay must be installed to convert the two wires into one for Nest compatibility. In addition the dehumidifier or humidifier must be configured correctly in the thermostat’s Pro Setup menu.

5. Test your old thermostat again and contact a pro 

Make sure the system test is over, and check that your thermostat and system are working.

• If the System Test is still running on your thermostat, select Done on the display. 
• Check if your system is working normally and check the thermostat for a code.
  • If you see the same code, you should contact a pro to check your system.
  • If you see another code, start over to troubleshoot that code.

E help codes

E codes are critical and must be fixed as soon as possible. Your thermostat won’t allow you to control heating or cooling, and the message won’t go away until the cause has been fixed.

Look at the table below and select your specific help code then follow the troubleshooting steps. You can also contact a pro for other issues (including HVAC).

It's important to protect you, your system, and your thermostat. Turn off the power to your system at the fuse box before exposing or adjusting any wiring.

Nest Learning Thermostat 1st gen	Nest Learning Thermostat 2nd gen		Nest Learning Thermostat 3rd gen		Nest Thermostat E	Nest Thermostat
E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 E11 E12 E13 E14	E22 E23 E24 E25 E27 E28 E29 E30 E32 E33 E34 E35 E36	E37 E38 E39 E40 E41 E52 E53 E54 E55 E56 E57 E58 E66	E72 E73 E74 E75 E77 E78 E79 E80 E82 E83 E84 E85 E86	E87 E88 E89 E90 E91 E102 E103 E104 E105 E106 E107 E108 E116	E155 E157 E158 E159 E160 E162 E164 E169 E182 E183 E184 E188 E194 E195 E196	E255 E257 E258 E260 E264 E269 E294 E296 E297 E298 E299

 

N help codes

 Select your help code to go to the troubleshooting steps you need. You can also contact a local pro to help resolve your issue.

Nest Learning Thermostat 1st gen	Nest Learning Thermostat 2nd gen	Nest Learning Thermostat 3rd gen	Nest Thermostat E	Nest Thermostat
N1 N2 N3 N4 N5 N6 N7	N21 N22 N23 N24 N25 N26 N27 N28 N29	N71 N72 N73 N74 N75 N76 N77 N78 N79	N153 N154 N156 N159	N253 N254 N256 N259 N260 N261

TD help codes

Find your help code and click on the article to the right of the code to go to the troubleshooting steps you need. You can also a local pro for other issues (including HVAC).

Help code			Troubleshooting
TD001 TD007 TD011 TD015 TD019 TD022	TD005 TD008 TD012 TD016 TD020	TD006 TD010 TD014 TD017 TD021	These codes means your thermostat is having problems connecting to Wi-Fi or to your app. Use the article below to troubleshoot your issue. Troubleshoot when your Nest thermostat is offline
TD003 TD004	TD009 TD018	TD023 TD030	Help codes that can occur when adding your thermostat to the app. Use the article below to troubleshoot your issue. Troubleshoot a TD003, TD004, TD009, TD018, TD023, or TD030 help code for Nest thermostat

M error codes

Find your help code below, and follow the link to troubleshoot. 

Help code	Troubleshooting
M1	How the Nest thermostat helps prevent Legionella bacteria
M2	Troubleshoot Farsight weather
M5	How to tell what kind of heating system you have
M6	Learn more about Furnace Heads-Up
M7	Learn about Emergency Heat
M8	Learn about Pro Setup
M9	How to tell if your system is Nest thermostat compatible
M10	Contact support
M11	Learn about the Nest thermostat’s star connector
M12	Troubleshooting when a Nest Temperature Sensor isn't in a good spot
M13	Troubleshoot E10, E30, E66, E80, E116, E160, E196 and M13 codes
M14	How to control your Nest thermostat with the app
M15	Troubleshoot an M15 code on a Nest thermostat
M16	Troubleshoot a Works with Nest connection
M17	Troubleshoot when your Nest thermostat is offline
M18	Learn about Rush Hour Rewards
M19	Change Nest thermostat batteries
M21	Troubleshoot when your Nest thermostat is offline
M22	Troubleshoot when your Nest thermostat is offline
M23	Thermostat wire undetected or unconfigured
M24	Contact the support team to help with this issue

W Error codes

Help code	Troubleshooting
W1 The Nest thermostat can't continue to connect to your Wi-Fi network.	Your Wi-Fi router may not fully support a Wi-Fi standard known as power saving mode. Wi-Fi routers that are incompatible with Nest products
W2 Failed to connect.	Your Wi-Fi router may have security settings enabled that prevent your Nest thermostat from connecting. How to find your Nest product's MAC address and add it to your router's whitelist
W3 Failed to connect.	Your Wi-Fi router is not providing a network IP address to your Nest thermostat. Troubleshooting a “Failed to connect” code
W4 Failed to connect.	The Nest thermostat is connected to your wireless network but not to the Internet. Troubleshooting a “Failed to connect” code
W5 Failed to connect.	Your Nest thermostat can't connect to Wi-Fi. Troubleshoot a Nest thermostat w5 code

H help codes

You'll see H help codes if your home has one of the following systems.

• Domestic hot water tank
• OpenTherm system
• Condensing boiler
• District or collective heating
• Fil pilote

Manually turn on heat, if needed

You can manually turn on your heat with the Heat Link while you troubleshoot so you can stay comfortable. If your thermostat controls your domestic hot water tank, your hot water will also turn on.

Press the button on your Heat Link to turn heating on or off while we work on your thermostat. The heating light will turn green to let you know the heat is on.

• Thermostat E - Press the button twice
• 3rd and 2nd gen thermostat - Press the button once

Find your code

Select the help code that you see on your thermostat for specific troubleshooting steps to fix the issue.

Learning Thermostat	Thermostat E
H1 H2 H71 H72 H73	H151 H152 H153 H155 H156 H157 H158

H1, H71, or H151

If you see this code, your thermostat can’t connect to your Heat Link to control your heating. In addition, the Heat Link's status light will be yellow when it’s disconnected from your thermostat.

1. Restart the Heat Link
   • Hold down the Heat Link’s button until its light turns off. It should take about ten seconds.
   • Release the button and wait for your Heat Link to restart.
   • The status light will turn green if it re-connects to your thermostat. If the status light is yellow, continue to step 2.
2. Move your thermostat and test the connection
   Your thermostat may be a bit too far away from the Heat Link or there may be something interfering with the wireless connection.Check that there isn’t anything physically between your Heat Link and thermostat, like a large mirror or refrigerator. Large objects made of metal or other dense materials can block wireless signals.
   • If your thermostat is on a stand
     • Try moving it closer to where your Heat Link is installed.
     • Now, check the wireless connection.
       • On your thermostat go to Settings > Equipment. Then select Continue > Heat Link > Test.
       • If the test fails, move your thermostat again and re-test. Sometimes moving your thermostat a few centimetres can make a big difference.
   • If your thermostat is mounted on the wall try moving the Heat Link. 
     • Before you move the Heat Link, turn off the power to your system at the fuse box.
     • Move the Heat Link so it is at least 1 m away from the boiler or other large metal objects.
     • After you move the Heat Link, turn the power to your system back on.
3. Reset the Heat Link to defaults

   Thermostat E

   Important: When you reset Heat Link for Nest Thermostat E to factory defaults, it will remove Heat Link from the app. You'll need to set up your Heat Link from scratch again.

   1. Remove your heat link from the Nest app. Remove your Heat Link from your account in the app
      • From the home screen, tap on the Heat Link
      • Tap Settings
      • Select Remove Heat Link
   2. Press and hold Heat Link's button until the status light turns solid yellow (about 15 seconds). Release the button.
   3. When the factory reset is complete, the status light will pulse blue to let you know.
   4. Reconnect your Heat Link to the app:
      • Remove Heat Link's cover so that you can see the QR code on top of the battery compartment.
      • In the app, go to Settings Add product.
      • Follow the on-screen instructions to scan the QR code and add Heat Link back to the app. When asked, tell the app that Heat Link is already installed, which lets you skip the instructions about installing it on your wall.

   3rd gen Learning Thermostat

   1. Press and hold Heat Link's button for about 20 seconds. The Heat Link's status light will turn off, then it will start quickly blinking yellow. Release the button.
   2. When the factory reset is complete, the Heat Link's status light will pulse blue.
   3. Normally, a Heat Link should automatically reconnect to your Nest thermostat after you reset it to factory defaults. Wait a few moments and then check your thermostat to confirm.
      • If your thermostat asks for a pairing code, look on the bottom of Heat Link for the 6-digit code.
      • If your thermostat is showing a code, go back to the beginning of this troubleshooter to troubleshoot that code.

   2nd gen Learning Thermostat

   1. Press and hold Heat Link's button for 20 seconds.
   2. While you're holding the button, Heat Link's status light will turn off, then it will start quickly blinking green and yellow. Release the button.
   3. When the factory reset is complete, Heat Link's status light will blink green and yellow.
   4. Normally, Heat Link should automatically reconnect to your Nest thermostat after you reset it to factory defaults. Wait a few moments and then check your thermostat to confirm.
      • If your thermostat asks for a pairing code, look on the bottom of Heat Link for the 6-digit code.
      • If your thermostat is showing another code, go back to the beginning of this troubleshooter to troubleshoot that code.
4. Stop wireless interference from other electronics
   Other electronic devices in your home that use a 2.4 GHz wireless signal may create interference with your Heat Link. This includes devices like cordless phones, baby monitors, microwave ovens, or wireless security cameras. 
   • Try turning off these devices one by one to see if your thermostat and Heat Link are then able to establish a wireless connection.
   • If one of these devices is causing interference, try moving it further away from the Heat Link or thermostat if possible and then recheck the connection. Go here to learn about wireless interference.

Contact a Nest Pro

If you’re still not able to fix the problem, contact a Nest Pro, who can properly diagnose your heating system and your Nest thermostat.

H2, H72, or H152

You’ll see this code if your thermostat lost power. How you troubleshoot this code depends on if your thermostat is on a stand or installed on the wall.

If your thermostat is on a stand

Make sure that the Nest power cable is fully inserted into the power plug and that the plug has been pushed all the way into the wall socket. Check that the wall socket is switched on. Note: We recommend plugging your thermostat into a socket that isn’t controlled by a wall switch to prevent accidentally switching it off. You can also double check that the socket is delivering power by plugging in a lamp or other electronic device and turning it on.

 

If your thermostat is on the wall

Make sure the thermostat display is completely attached to the base. If it’s not, push it down on the base until you hear it click. Try moving the Heat Link.  Before you move the Heat Link, turn off the power to your system at the fuse box. Move the Heat Link so it is at least 1 m away from the boiler or other large metal objects. Also check that there isn’t anything directly between your Heat Link and thermostat, like a large mirror or refrigerator. After you move the Heat Link, turn the power to your system back on.

 

Check the system power

1. Check the fuse. It’s possible that the fuse controlling power to your system isn’t properly seated or is blown. Turn off the power to your system, then check the fuses. Re-seat or replace it as necessary. Refer to the manufacturers manual or website for exact instructions and safety precautions.
2. Make sure that the switch is set to 'on'. Sometimes fuse switches can look like they’re on, but haven’t been flipped on all the way.
   • Try flipping the switches that control power to the Heat Link and your thermostat off and then on again.
   • You can also check power to the socket that the Nest thermostat is using by plugging in a lamp or other electronic device and turning it on.

Contact a Nest Pro

If you’re still not able to fix the problem, contact a local pro, who can properly diagnose your heating system and your Nest thermostat.

H73 or H153

You’ll see this code if your thermostat can’t detect your system’s OpenTherm. How you troubleshoot these codes depends on whether you see it during installation or after installation.

If you see the code during installation

Verify that your heating system supports OpenTherm. Check your system’s documentation or contact the manufacturer. There may also be an OpenTherm logo  somewhere on your system. Make sure that the Heat Link is correctly wired. Check your Heat Link’s wiring against the wiring diagrams in the installation guide. If you need to move any wires, turn off the power to the Heat Link and your system at the fuse box before exposing or adjusting any wiring. If your system does not support OpenTherm, you will need to select On/Off boiler control instead of OpenTherm. Open Settings Equipment  Pro Setup to change the boiler control setting.

If you see the code after installation

While you’ll usually see this code during or right after thermostat installation, it can sometimes occur after you’ve been using your thermostat for a while.

1. Check that the power to your boiler hasn’t been turned off.
2. If the switch controlling power to your boiler is on, but it’s not receiving power, contact a local Nest Pro to check your system.

Contact a Nest Pro

If you’re still not able to fix the problem, contact a local pro, who can properly diagnose your heating system and your Nest thermostat.

H155

An H155 help message on your thermostat says 'Your Heat Link went offline when the batteries were low'.

• Pull off the Heat Link cover and replace the batteries with new L91 Energiser Lithium AA batteries. 
  • Important: Do not use regular alkaline batteries.
• The Heat Link should automatically reconnect to your thermostat when new batteries are installed.

Contact a Nest Pro

If you’re still not able to fix the problem, contact a local pro, who can properly diagnose your heating system and your Nest thermostat.

H156

Your system is wired for and compatible with OpenTherm, but the OpenTherm option wasn’t selected during setup.

On your thermostat, go to Settings Equipment. Then change your boiler control to OpenTherm.

Contact Nest support

If you followed the steps above and you still see the message on your thermostat, contact support for more help.

H157

You’ll see this code if you’ve removed the Heat Link from the app.

1. If your Heat Link can’t be connected to the app, reset it to factory defaults.
2. Reconnect the Heat Link to your thermostat with the app.
   • Go to Settings Add product and follow the instructions to add it to the app.
   • When prompted, enter the pairing code from the Heat Link in the thermostat display.
3. In some cases, you may need to enter the Heat Link’s pairing code into your Nest thermostat. 

Note: To find the code, pull off the Heat Link’s cover and look for the code near the left screw hole. It’s a combination of six letters and numbers.

Contact Nest support

If you followed the steps above and you still see the message on your thermostat, contact support for more help.

H158

You’ll see this code if you’ve removed the Heat Link from your account, and your thermostat disconnected from the app. Reset your thermostat to factory default, then reconnect it and the Heat Link to the app.

1. Press your thermostat ring to open the Quick View menu.
2. Choose Settings .
3. Turn the ring to Reset and press to select.
4. Select All Settings to reset your thermostat to factory settings.
5. Begin thermostat setup with the app to connect it and your Heat Link to your account again.
   • Tap the Settings  icon on the app home screen.
   • Select Add product to start thermostat setup.

Contact Nest support

If you followed the steps above and you still see the message on your thermostat, contact support for more help.

What your help code means

E help codes

This table shows you which wire or wires you'll need to troubleshoot.

Help code	How to troubleshoot
E1 Common wire ("C" wire) is required.	Troubleshoot C wire
E2, E22 and E72  No power wires detected. Rc or Rh wire required.	Troubleshoot power
E3, E23 and E73 No power to Rc wire detected.	Troubleshoot power
E4, E24 and E74 No power to Rh wire detected.	Troubleshoot power
E5, E25, E75, E155 and E255 No heating or cooling detected. W1 or Y1 wire is required.	Troubleshoot wiring
E6  Too many wires detected. Please remove at least one of O/B, W1, Y1 or AUX.	Troubleshoot wiring
E7, E27, and E77 Y1 wire not detected. A heat pump requires a Y1wire.	Troubleshoot wiring
E8, E28 and E78 Additional wire(s) required. W2/AUX detected by itself.	Troubleshoot wiring
E9, E29, E79 and E159 No power to C wire detected.	Troubleshoot power
E10, E30, E66, E80, E116, E160, E196 and E296 No power to Y1 wire detected (cold weather shutoff).	Troubleshoot Y wire
E11 Heat pump wire O/B detected. No heat pump system present.	Troubleshoot wiring
E12, E32, E82 and E162 No power to W1 wire detected.	Troubleshoot power
E13, E33, E36, E37, E38, E83, E86, E87 and E88 A heat pump can have at most one auxiliary heat wire.	Troubleshoot wiring
E14, E34, E84, E164 and E264 Dual fuel requires an alternate heat wire.	Troubleshoot wiring
E35 and E85 Dual fuel can have at most two alternate heat wires.	Troubleshoot wiring
E39, E89, E169 and E269 Y2 wire without Y1 wire.	Troubleshoot wiring
E40 and E90 W3 wire without W2/AUX to wire.	Troubleshoot wiring
E41 and E91 E wire without O/B wire.	Troubleshoot wiring
E52, E53, E54, E55, E56, E57, E58, E102, E103, E104, E105, E106, E107, E108, E182, E183 and E188 The Nest thermostat has an overcurrent error.	Troubleshoot wiring
E109 G2 detected. G1 wire is also required.	Troubleshoot wiring
E110 G2 wire detected. Remove W2/AUX wire.	Troubleshoot wiring
E111 G2 wire detected. Remove E wire.	Troubleshoot wiring
E112 G wire detected. G1 and G2 also required.	Troubleshoot wiring
E113 G2 and O/B wire conflict.	Troubleshoot wiring
E157 Y1 wire not detected.	Troubleshoot wiring
E158 W1 wire not detected.	Troubleshoot wiring
E184 Check G wire	Troubleshoot wiring
E194 R wire not detected	Troubleshoot wiring
E195 No power to R wire detected.	Troubleshoot power
E257 Heat pump requires Y1 wire	Troubleshoot wires in Home app
E258 W2 wire requires W1	Troubleshoot wires in Home app
E260 No power to Y1	Troubleshoot power
E264 Dual fuel requires an alternate heat wire.	Troubleshoot wires in Home app
E269 Y2 wire requires a Y1 wire	Troubleshoot wires in Home app
E294 R wire is required	Troubleshoot wires in Home app
E296 No power to Y1 wire detected (cold weather shutoff).	Troubleshoot Y wire
E297 C wire or Y1 wire required	Troubleshoot C wire
E298 No system power	Troubleshoot power
E299 Contact support	Contact support

N codes

This table shows you which wire or wires you'll need to troubleshoot.

Help code	How to troubleshoot
N1, N21 and N71 Power wire Rc detected. Not connected to equipment.	Troubleshoot low power
N2, N22 and N72 Power wire Rh detected. Not connected to equipment.	Troubleshoot low power
N3, N23, N73 and N153 No power to W1 wire detected.	Troubleshoot low power
N4, N24, N74 and N154 No power to Y1 wire detected.	Troubleshoot low power
N5, N25 and N75 No power to W2/AUX wire detected.	Troubleshoot low power
N6, N26, N76 and N156 No power to G wire detected.	Troubleshoot low power
N7, N27 and N77 No power to O/B wire detected.	Troubleshoot low power
N28 and N78 No power to Y2 wire detected.	Troubleshoot low power
N29, N79 and N159 No power to wire detected.	Troubleshoot low power
N253 No power to W1	Troubleshoot power
N254 No power to Y1	Troubleshoot Y wire
N256 No power to G	Troubleshoot power
N259 No power to *|OB	Troubleshoot power
N260 A C wire is recommended for your thermostat	Troubleshoot C wire
N261 Low power to C wire	Troubleshoot C wire

 

Troubleshooting steps

Your thermostat needs a C wire

These steps cover the following help codes: E1, E297, N261, N260

You might see this help code for one of the reasons below:

• The C wire isn’t providing enough power to your thermostat.
• Your thermostat might need a C wire to provide it with dedicated power.

1. Check your thermostat for a C wire

You can check your thermostat or your system for a C wire yourself, or contact a pro to check for you.

1. Turn off power to your system at the breaker box, fuse box or system switch.
2. Pull off the Nest thermostat display and check the C connector.
   • If there isn’t a wire, continue to “Check your system for a C wire”
   • If there is a wire in the C connector, check that the wire has the C wire label, then make sure it’s in all the way and the connector button is down.
     • You may need to strip the wire ends. There should be ⅓ to ½ inch of straight, corrosion-free copper wire exposed.
     • Put the thermostat display back on and press until it clicks into place. Then turn power to your system back on.

2. Check your system for a spare wire

Your system might have a spare wire that’s not connected to your thermostat that you may be able to use as a C wire. If there isn’t a spare wire, you’ll need to contact a pro to have one installed.

Important: These are advanced troubleshooting steps. Your HVAC system uses high voltage, which can be dangerous. If you need to open your HVAC system, be careful not to touch any of the components unless expressly instructed to do so.

If you got pro installation when you first installed your thermostat, you may want to contact your installer or find a local pro if you need any help.
 

1. Make sure to turn off the power to your HVAC system at the breaker box, fuse box, or system switch, if it isn’t off already.
2. If you found a spare wire, note the color of the wire.
3. On your HVAC system, look for a removable access panel. It may have a handle or latch, or you may need to remove some screws. 
   • Be careful not to touch any of the components inside your system except for the system wires. Some HVAC equipment has electrical components that store a charge like a battery. 
4. Check the board’s C terminal. If there’s no wire in it, look for the spare wire you found on the thermostat end and attach it.
5. Replace the access panel.
6. At your thermostat, connect the spare wire to the C connector. Make sure it’s in all the way and the connector button is down.
7. Press the display onto the base until it clicks into place and turn your system power back on.

Low power to thermostat

These steps cover the following help codes: N1, N21, N71, N2, N22, N72, N3, N23, N73, N153, N4, N24, N74, N15, N5, N25, N75, N6, N26, N76, N156, N7, N27, N77, N28, N78,N29, N79 N159, N261

You’ll see this code if one of the wires in your thermostat is receiving power, but it's less power than expected.

Turn off power to your system at the breaker box, fuse box or system switch. This helps prevent damage to your system and keeps you safe. Pull off the thermostat display. Check that all connectors with wires are down as pictured. If they aren’t, re-insert the wires. Press the connector button down and insert the wire as far as it will go. If the wire is in correctly, the button will stay down when you let it go. You may need to strip the wire ends. There should be ⅓ to ½ inch of straight, corrosion-free copper exposed. Press the display onto the base until it clicks into place and turn your system power back on.

 

If you still see the code on your thermostat, but your system is running normally, you can dismiss the message and continue to use your thermostat. The message shouldn’t pop up again after you dismiss it, however you may want to contact a pro to take a look at your system.

If you’ve completed all the troubleshooting steps above and your thermostat still isn’t working correctly, contact a local pro for more help.

Your HVAC system needs maintenance

These steps cover the following help codes: M6

If you see this code, that means there is a problem with your HVAC system. Contact a pro to service your system and fix this issue.

Check power to your Y wire

These steps cover the following help codes: E10, E30, E66, E80, E116, E160, E196, E296, M13, N254

You’ll see this code if your air conditioner has tripped a safety cut-out switch that prevents your air conditioner from turning on in very cold weather, or your system might need maintenance.

Go to Troubleshoot E10, E30, E66, E80, E116, E160, E196, M13, and N254 help codes to troubleshoot this issue.

Check your system power or wires

Troubleshoot power

You’ll see this code if your thermostat doesn’t detect power to a wire, or it can’t detect the wires in your thermostat.

1. Check the system power

First, make sure the power to your system is on. The power switch will usually be in your breaker box or fuse box, but in some homes it will look like a light switch near the heating or cooling equipment. 

1. There may be a single switch, or two switches: one for heating and one for cooling. Make sure the power is on for both then check your thermostat.
2. After you check the power, go to your thermostat and check if it’s working.

2. Check the thermostat wires

Important: Protect yourself and your thermostat and your system. Turn off power to your system and thermostat at the breaker or fuse box before exposing or adjusting any wiring.

1. Pull off the thermostat display.
2. Check that the wires are inserted correctly in the thermostat.

   Check that each wire is fully inserted into its connector and that every connector with a wire is down as shown. Check that each wire has ⅜ inch (6mm) of exposed wire. Turn the power to your system back on and check to see if your thermostat is working.

If you’ve completed all the troubleshooting steps above and your thermostat still isn’t working correctly, contact a local pro for more help.

Troubleshoot wiring

You’ll see this code if there is an issue with the wiring in your thermostat.

1. Check the system power

First, make sure the power to your system is on. The power switch will usually be in your breaker box or fuse box, but in some homes it will look like a light switch near the heating or cooling equipment. 

1. There may be a single switch, or two switches: one for heating and one for cooling. Make sure the power is on for both then check your thermostat.
2. After you check the power, go to your thermostat and check if it’s working.

2. Check the thermostat wires

Nest, check that your system’s wires are in the right connectors.

Important: Protect yourself, your thermostat and your system. Turn off power to your system and thermostat at the breaker or fuse box before exposing or adjusting any wiring.

1. Pull off the thermostat display.
2. Check that the wires are inserted correctly in the thermostat.

   Check that each wire is fully inserted into its connector and that every connector with a wire is down as shown. Check that each wire has ⅜ inch (6mm) of exposed wire.

3. Put the display back on the base and turn the power to your system back on.
4. Check to see if your thermostat is working. If it still doesn’t work, check that your system wires are connected to the right connectors. Use the wiring diagram the app gave you during setup to move the wires to the right connectors.
   • Turn off power to your system and thermostat at the breaker or fuse box.
   • If you don’t have the wiring diagram, refer to the picture of your thermostat wires that you took when it was installed. If you didn’t take a picture or can’t find it, follow these instructions to access your system’s control board and take a picture of the wires. Use this picture to enter the wires into the app.

     In the Nest app

     1. Open the Nest app.
     2. Use these steps to add the thermostat to the app to get the wiring diagram.
        • If you don’t have other products in the app
          • Tap Add product on the home screen and follow the app instructions. 
        • If you have other products in the Nest app 
          • Tap Settings  in the top right. 
     3. Select Add product.
     4. Follow the app instructions. Make sure you choose the Start installation even though you’ve already installed your thermostat.
     5. Follow the app instructions until the app asks you to enter your thermostat wires. Use the picture you took of your old thermostat’s wires or your control board wires as a reference.
     6. The app will give you a wiring diagram. Move the wires to the right connectors to match the wiring diagram. If you need to move wires, your thermostat may ask you a few questions.
        • Important: Make sure the wires have ⅓ to ½ inch (6mm) of copper exposed and that the wire connectors stay all the way down.
     7. After you have the wiring diagram, you can exit device setup.

     In the Home app

     1. Open the Home app.
     2. Tap Add + at the top left of the home screen.
     3. Tap Set up device and follow the app instructions until you get to the wiring step. 
        • Use the picture of your old thermostat’s wiring to enter the wires into the app.
        • After you have the wiring diagram, you can exit device setup. 
     4. Move the wires to the right connectors to match the wiring diagram.
        • Make sure the wires have ⅓ to ½ inch (6mm) of copper exposed, the wire is fully inserted into the connector, and that the wire connector button stays down.
     5. Replace the thermostat display and turn your system power back on.
5. Turn power to your system back on at the breaker or fuse box.

If you’ve completed all the troubleshooting steps above and your thermostat still isn’t working correctly, contact a local pro for more help.

 

Check wire configuration in the Home app

These steps cover the following help codes: E255, E257, E258 E264, E269, E294

If you didn't see a code, your thermostat will show you a link to let you know which wire you need to check. For example, if you see "g.co/nest/needWY" you need to check your W or Y wire.

You’ll see this code if the wires in your thermostat weren’t configured properly in the Home app. You’ll need to reset your thermostat to the factory default and add it back to the Home app.

1. Open the Home app.
2. Select your thermostat.
3. Open Settings. 
4. Tap Remove device Remove. 
5. On your thermostat, tap on the right side to open the menu.
6. Swipe to Settings and tap to open.
7. Scroll to Factory reset.
8. Choose Reset and tap.
9. Select Yes and tap.

Next, add your thermostat back to the Home app. Tap Add + at the top left of the home screen and follow the instructions on screen. Pay extra attention to the instructions when you reenter your wiring info.

If it's still not working, check that your system wires are connected to the right connectors. Use the wiring diagram the app gave you during setup to move the wires to the right connectors.

If you don’t have the wiring diagram, refer to the picture of your thermostat wires that you took when it was installed. If you didn’t take a picture or can’t find it, follow these instructions to access your system’s control board and take a picture of the wires. Use this picture to enter the wires into the app.

1. Open the Home app.
2. Tap Add + at the top left of the home screen.
3. Tap Set up device and follow the app instructions until you get to the wiring step. 
   • Use the picture of your old thermostat’s wiring to enter the wires into the app. 
4. Move the wires to the right connectors to match the wiring diagram.
   • Make sure the wires have ⅓ to ½ inch of copper exposed, the wire is fully inserted into the connector, and that the wire connector button stays down.
5. Replace the thermostat display and turn your system power back on.
6. Turn power to your system back on at the breaker or fuse box.

Hot weather troubleshooting

These steps cover the following help codes: E3, E4, E23, E24, E73, E74 or E195

If your Nest thermostat suddenly started showing one of these codes during the hot summer months, visit the following link to learn how to help fix it:

• Troubleshoot E3, E4, E23, E24, E73, E74 and E195 help codes

Contact support

These steps cover the following help codes: E299, M24

You’ll need to contact Google Nest customer support to help resolve this issue. 

• Have the help code and your thermostat’s serial number ready to give to the support agent. 
• To find your thermostat’s serial number, pull the display off the base and flip it over. The serial number is above the QR code on the back of the display.