Troubleshoot Nest thermostat T error codes during a System Test

If you see an error message on your thermostat that has a code beginning with H, N or T followed by a number, here are some steps that you can take to help fix them.

Manually turn on heat, if needed

Press the button on your Heat Link to manually turn on heating:

Google Nest Thermostat E: Press Heat Link’s button twice
3rd and 2nd gen Google Nest Learning Thermostat: Press Heat Link’s button once

The heating light will turn green to confirm that the heating has been turned on. This way, you can stay comfortable while you troubleshoot connection problems. If your thermostat controls your hot water tank, your hot water will also turn on.

Note: Press the Heat Link's button again to turn off heating (press twice for Nest Thermostat E).

Find your error

Select your thermostat below, then select the error code that you see on your thermostat for specific troubleshooting steps to fix the issue.

If you don’t see an error code on your thermostat, please search our library of help articles for help with other issues.

Nest Learning Thermostat

H1 or H71

An H1 or H71 error message says 'Nest can’t connect to Heat Link and won’t be able to control your heating'. In addition, the Heat Link's status light will be yellow when it’s disconnected from your thermostat.

Restart the Heat Link
1. Hold down the Heat Link’s button until its light turns off. It should take about ten seconds.
2. Release the button and wait for your Heat Link to restart.
3. The status light will turn green if it re-connects to your thermostat. If the status light is yellow, continue to step 2.
Move your thermostat and test the connection

Your thermostat may be too far away from the Heat Link or there may be something interfering with the wireless Thread connection.
1. If your thermostat is mounted on a stand (not the wall), try moving it a bit closer to where your Heat Link is installed.
2. Check that there isn’t anything 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.
3. 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.
Check your Heat Link installation

The wireless thermostat connection can be blocked if your Heat Link is installed too close to your boiler or hot water tank. Make sure that the Heat Link is installed at least 1 m (3.3 ft) away from your boiler or heating system. Reposition it if possible.

Caution: 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.
Reset the Heat Link to defaults

Try resetting the Heat Link and then reconnecting it to your thermostat. For complete instructions, please see How to restart the Heat Link or reset it to factory defaults.

In some cases, you may need to re-enter the Heat Link’s pairing code on your Nest Learning Thermostat. The code is a combination of six letters and numbers.
- 3rd-gen Heat Links have the pairing code on the bottom
- 2nd gen Heat Links have the pairing code underneath the cover, near the left screw hole.
Stop wireless interference from other electronics
1. Other home products that use a 2.4 GHz wireless signal may cause interference. This includes cordless phones, baby monitors, microwave ovens and wireless security cameras. Try turning off these electronics one by one to see if your Google Nest Learning Thermostat and Heat Link are then able to establish a wireless connection.
2. Once you have found out what’s causing the interference, try moving it further away from the Heat Link or Google Nest Learning Thermostat if possible and then recheck the Google Nest Learning Thermostat connection.
Note: Switching from a wireless product to one that uses cables, such as a corded phone, can solve interference issues.

Learn about wireless interference and how to troubleshoot it >

H2 or H72

An H72 error message says 'The power to this thermostat is off'. Note that this error can take a few minutes to appear after power has been cut, so you may not see it immediately.

1. Check the thermostat power cable, plug and power socket.

If you have a Google Nest Learning Thermostat on the Nest 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.

2. Make sure that the display and power cable are fully seated.

Pull the display straight off.
Check that the power cable is fully inserted into the
power port and is routed correctly through the groove in
the base of the thermostat.
Line up the display connectors and press the display
firmly back onto the base. You will hear a click and the
display will lie flush with the base when it’s properly seated.

Incorrect and correct ways to mount the display

3. Check the fuse box

Check the fuse: It’s possible that the fuse controlling power to your system isn’t properly seated or is blown. Re-seat or replace it as necessary.
Make sure that the switch is set to 'on': Sometimes fuse switches can be tricky: you may think that you've flipped a switch back on, but it might not have been pushed all the way.
- Try flipping the switches that control power to Heat Link and your thermostat off and then on again.
- You can also check power on the socket that the Nest thermostat is using by plugging in a lamp or other electronic device and turning it on.

4. Contact a Nest Pro

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

H73

N80

An N80 error message says, 'OpenTherm requires a wireless connection but wireless isn’t detected'.

Restart the Heat Link
1. Hold down the Heat Link’s button until its light turns off. It should take about ten seconds.
2. Release the button and wait for your Heat Link to restart.
3. The status light will turn green if it re-connects to your thermostat. If the status light is yellow, continue to step 2.
Move your thermostat and test the connection

Your thermostat may be too far away from the Heat Link or there may be something interfering with the wireless Thread connection.
1. If your thermostat is mounted on a stand (not the wall), try moving it a bit closer to where your Heat Link is installed.
2. Check that there isn’t anything 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.
3. 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.
Check your Heat Link installation

The wireless thermostat connection can be blocked if your Heat Link is installed too close to your boiler or hot water tank. Make sure that the Heat Link is installed at least 1 m (3.3 ft) away from your boiler or heating system. Reposition it if possible.

Caution: 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.
Reset the Heat Link to defaults

Try resetting the Heat Link and then reconnecting it to your thermostat. For complete instructions, please see How to restart the Heat Link or reset it to factory defaults.

In some cases, you may need to re-enter the Heat Link’s pairing code on your Google Nest Learning Thermostat. The code is a combination of six letters and numbers.
- 3rd-gen Heat Links have the pairing code on the bottom
- 2nd gen Heat Links have the pairing code underneath the cover, near the left screw hole.
Stop wireless interference from other electronics
1. Other home products that use a 2.4 GHz wireless signal may cause interference. This includes cordless phones, baby monitors, microwave ovens and wireless security cameras. Try turning off these electronics one by one to see if your Google Nest Learning Thermostat and Heat Link are then able to establish a wireless connection.
2. Once you have found out what’s causing the interference, try moving it further away from the Heat Link or Google Nest Learning Thermostat if possible and then recheck the Google Nest Learning Thermostat connection.
Note: Switching from a wireless product to one that uses cables, such as a corded phone, can solve interference issues.

Learn about wireless interference and how to troubleshoot it >

T05, T06 or T07

You’ll see a T05, T06 or T07 error message when running a system test after you first install your thermostat.

Important: Troubleshooting for each of these errors is the same in most cases but there are specific troubleshooting steps for certain errors in some steps.

Run the test longer
- 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 skirting board 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.
- The System Test will run for 35 minutes before automatically stopping. Select Keep Testing on your thermostat if needed, or restart testing by going to Settings Equipment on your thermostat. Select Continue and then Test.
Make sure that your boiler and Heat Link have power

Check that the Heat Link light is on, and your boiler’s light or screen is on too. If they aren’t receiving power:
- Check that the breaker switch or fuse that controls power to your system is set to on.
  
  Caution: It's important to protect you, your system and your thermostat. 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. They may have a separate switch which also needs to be set to on.
- In some homes it’s common to turn off the boiler for the warm seasons and heating is no longer needed. So it can be helpful to double check that the boiler and the breaker switch connected to the boiler are on, and that the boiler has power.
Check that the Heat Link is wired correctly

WARNING ELECTRIC SHOCK HAZARD: Failure to turn off the power may result in serious electric shock, injury and death.
1. Turn off power to your system at the breaker or fuse box.
2. Pull off the Heat Link cover.
3. Make sure that the wires are connected to your Heat Link correctly. Follow the installation guide’s wiring diagrams &emdash; it was included in the box with your thermostat. You can also download a PDF version of the thermostat installation guide here.
4. If the wires are in the right Heat Link connectors:
  - Check that each wire is fully inserted into its connector and that every connector with a wire is drawn as shown.
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. Select Continue and then Test.
7. If there are still issues, have a local Nest Pro check your installation.
Steps for specific system types

Check to see if anything below applies to your system or error, then restart the system test if needed.
- If your system has radiators (T06 error): Make sure that the radiator valves are fully open so that hot water from the boiler can enter the radiators. The valves may have been closed if the season is warm and heating isn’t needed.
- Make sure that your programmer isn’t interfering with boiler control: If you had a programmer before installing the Google Nest Learning Thermostat, it’s important that the heating channel is disabled so that it doesn’t interfere with heating.
  
  What to do with a programmer after installing a Nest thermostat >
- Check your heating lever valve: If you have a manual valve to turn on heating, make sure that the valve lever is in the on position, otherwise hot water won’t flow through the heating pipes.
- If you have a Fil Pilote system: You should have your thermostat professionally installed in order to keep you safe and avoid damaging your system or your Google Nest Learning Thermostat. Your Nest Pro may need to install an additional Fil Pilote diode (sold separately) depending on your current system. Learn more about Fil Pilote and Nest.
Reinstall your old thermostat and contact a Nest Pro

Some systems are complex and difficult to set up correctly. In addition, there may be an issue with your system. For instance, sometimes a system fuse gets blown if thermostat wires make contact with each other during installation.
1. If you’ve followed all the troubleshooting steps above, reconnect your old thermostat to your system.
2. Then contact a local Nest Pro to help you get your Google Nest Learning Thermostat connected to your system and set up correctly.

Nest Thermostat E

H151

An H151 error message on your thermostat says 'Nest can't connect to the Heat Link and can't control your heat'. In addition, the Heat Link's status light will be yellow when it’s disconnected from your thermostat.

Restart the Heat Link
1. Hold down the Heat Link’s Nest button until it’s light turns off. It should take about eight seconds.
2. Release the button and wait for your Heat Link to restart.
3. The status light will pulse blue then turn green when it reconnects to your thermostat. If the status light is yellow, continue to step 2.
Move your thermostat and test the connection

Your thermostat may be too far away from the Heat Link or there may be something interfering with the wireless Thread connection.
1. Try moving your thermostat a bit closer to where your Heat Link is installed.
2. Check that there isn’t anything 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.
3. 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.
Reset the Heat Link to defaults

Try resetting the Heat Link and then reconnecting it to your thermostat. For complete instructions, please see How to restart the Heat Link or reset it to factory defaults.

In some cases, you may need to enter the Heat Link’s pairing code into your Nest thermostat. Pull off the Heat Link’s cover. Remove the wire cover’s screw. You’ll find the code on the back of the wire cover. It’s a combination of six letters and numbers.
Stop wireless interference from other electronics
1. Other home products that use a 2.4 GHz wireless signal may cause interference. This includes cordless phones, baby monitors, microwave ovens and wireless security cameras. Try turning off these electronics one by one to see if your Google Nest Learning Thermostat and Heat Link are then able to establish a wireless connection.
2. Once you have found out what’s causing the interference, try moving it further away from the Heat Link or Google Nest Learning Thermostat if possible and then recheck the Google Nest Learning Thermostat connection.
Note: Switching from a wireless product to one that uses cables, such as a corded phone, can solve interference issues.

Learn about wireless interference and how to troubleshoot it >

H152

H153

H155

H156

H157

H158

T05, T06 or T07

You’ll see a T05, T06 or T07 error message when running a system test after you first install your thermostat.

Important: Troubleshooting for each of these errors is the same in most cases but there are specific troubleshooting steps for certain errors in some steps.

Run the test longer
- 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 skirting board 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.
- The System Test will run for 35 minutes before automatically stopping. Select Keep Testing on your thermostat if needed, or restart testing by going to Settings Equipment on your thermostat. Select Continue and then Test.
Make sure that your boiler and Heat Link have power
- Check that the breaker switch or fuse that controls power to your system is set to on.
  
  Caution: It's important to protect you, your system and your thermostat. 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. They may have a separate switch which also needs to be set to on.
- In some homes it’s common to turn off the boiler for the warm seasons and heating is no longer needed. So it can be helpful to double check that the boiler and the breaker switch connected to the boiler are on, and that the boiler has power.
- Make sure that your Heat Link’s batteries have a sufficient charge. Simply press the button on the Heat Link. If its light doesn’t turn on, you will need to replace the batteries with new L91 Energiser Lithium AA batteries. Do not use regular alkaline batteries.
Check that the Heat Link is wired correctly

You will need to begin setup with the app again to check the wiring:
1. Turn off power to your system at the breaker or fuse box.
2. Pull off the Heat Link cover.
3. Make sure that the wires are connected to your Heat Link correctly:
  - Reset your thermostat to defaults
  - Reset the Heat Link to defaults
  - Remove your thermostat and Heat Link from the app.
  - Then begin setup with the app again. Make sure to answer the app’s questions accurately and closely follow the wiring instructions.
4. If the wires are in the right Heat Link connectors:
  - Check that each wire is fully inserted into its connector and that all wires are secured with the screws.
  - Check that each wire has 6 mm (⅜") of exposed wire.
  - Make sure that there is no corrosion or rust on the wires. Cut and strip the ends to expose fresh wire if needed.
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. Select Continue and then Test.
7. If there are still issues, have a local Nest Pro check your installation.
Steps for specific system types

Check to see if anything below applies to your system or error, then restart the system test if needed.
- If your system has radiators (T06 error): Make sure that the radiator valves are fully open so that hot water from the boiler can enter the radiators. The valves may have been closed if the season is warm and heating isn’t needed.
- Make sure that your programmer isn’t interfering with boiler control: If you had a programmer before installing the Google Nest Learning Thermostat, it’s important that the heating channel is disabled so that it doesn’t interfere with heating.
  
  What to do with a programmer after installing a Nest thermostat >
- Check your heating lever valve: If you have a manual valve to turn on heating, make sure that the valve lever is in the on position, otherwise hot water won’t flow through the heating pipes.
- If you have a Fil Pilote system: You should have your thermostat professionally installed in order to keep you safe and avoid damaging your system or your Nest thermostat. Contact a local Nest Pro to help you get your Nest thermostat set up correctly. Learn more about Fil Pilote and Nest.
Reinstall your old thermostat and contact a Nest Pro

The Google Nest Thermostat E is designed for DIY installation, but some systems are complex and difficult to set up correctly. In addition, there may be an issue with your system.

For instance, sometimes a system fuse gets blown if thermostat wires make contact with each other during installation.
1. If you’ve followed all the troubleshooting steps above, reconnect your old thermostat to your system.
2. Then contact a local Nest Pro to help you get your Google Nest Learning Thermostat connected to your system and set up correctly.

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Troubleshoot Nest thermostat T error codes during a System Test

Manually turn on heat, if needed

Find your error

Nest Learning Thermostat

H1 or H71

H2 or H72

H73

N80

T05, T06 or T07

Nest Thermostat E

H151

H152

H153

H155

H156

H157

H158

T05, T06 or T07

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