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Typically, there isn't cause for concern if your Nest thermostat or heat link is emitting a flashing blue light.

However, if the blue light doesn’t go away, it can indicate an issue with connectivity, whether that’s Wi-Fi or the thread network.

So in this guide, I’ll show you how to troubleshoot this issue for both Heat links and Nest thermostats below.

Note: Nest Thermostats in Europe come with a Heat Link device. If you are in the US, you can ignore all instructions related to the Heat Link.

Generally, a flashing blue light on your Nest thermostat indicates that it’s trying to start up or maintain a connection with the Wi-Fi router, smart device, or Heat Link. 

The flashing blue light can also be found in Heat Links, especially when they are trying to pair up with your thermostat.

So let’s talk about some of the more specific situations where you would encounter a flashing blue light below.

Nest Learning Thermostats

Smart Thermostat with intelligent scheduling features

Nest Learning Thermostats

In the case of the Nest Learning Thermostat, the flashing blue light usually pops up during a reboot procedure. It is completely normal and you only have to wait a couple of minutes until the device boots up.

However, if the Nest thermostat is not responding or keeps flashing blue indefinitely, it might be facing an issue during initialization, so keep reading as I’ve listed a troubleshooting guide below.

Heating Programmer stand-in for Nest Thermostat E Models

Heat Link Nest Thermostat E

The Heat Link connected to your Nest Thermostat E will usually indicate a pulsing or rapidly flashing blue light in certain situations. 

  • Pulsing Blue Light: This occurs when the Heat Link is restarting and trying to create a connection with your Nest thermostat or the Nest app.
  • Rapidly Blinking Blue Light: The Heat Link picks up the pace with the blue blinking light whenever it’s performing a software update.

In either of these situations, your Heat Link can get stuck, especially when it runs into connectivity issues, so make sure your devices have a strong signal and that your Wi-Fi router can connect to the internet.

Heating Programmer Adapter for 3rd Gen Nest Learning Models

3rd Gen Heat Link

In this model, the Heat Link will start pulsing blue (slowly) when it’s in pairing mode. 

So if you encounter this indicator with your 3rd gen Nest Learning Thermostat, make sure to bring the thermostat closer to the Heat Link so it can pair up successfully. 

How to Fix A Flashing Blue Light on a Nest Thermostat

Firstly, let's talk about what you can do to fix a Nest thermostat that's indicating a flashing blue light.

At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.

1. Check the Thermostat Wiring

If the flashing blue light doesn't go away on its own, you can start by diagnosing the thermostat wiring strip. Here's how:

  1. First, remove the thermostat display from the wall mount
  2. Then, take a look at the thermostat wiring, and check the wires for any signs of damage
  3. After that, make sure the connections are tight, simply tug on each wire and make sure they are secure
  4. If not, try reconnecting the wires, making sure they are installed in the proper terminals.
  5. Check the pins and terminals as well, making sure they aren't bent, damaged, or filled up with dust or debris. 
  6. Try cleaning any dust or if possible, straightening and bent pins
  7. After the wiring is secure, reconnect the thermostat and see if the flashing blue light goes away
Thermostat Wiring
Make sure the wires are in the correct terminals and they aren't damaged

2. Manually Restart the Nest Thermostat

If the thermostat wiring isn’t the problem, you can try manually restarting the Nest thermostat. 

For Nest Thermostat (2020 Model):

  1. Pull the thermostat from its wall mount
  2. Take out both AAA batteries
  3. Wait a couple of minutes
  4. Then reinstall the batteries 
  5. After that, install your thermostat back on the wall mount. Make sure it clicks into place.
  6. Wait several minutes until the device boots up

For Nest E and Nest Learning Models

  1. Press down on the thermostat ring button for 10 seconds. Then release
  2. After that, press the ring button again. Don’t hold.
  3. Wait for the screen to power up. This will indicate that the device is rebooting.

3. Replace or Recharge the Batteries

To fix any power issues, I recommend replacing the batteries with fresh ones or recharging the internal batteries on your Nest thermostat. 

This will help fix any power issues and get the thermostat back up and running. 

Also, if possible, I highly recommend setting up your thermostat with a C-wire for more stable power.

4. Fix Wi-Fi Signal Strength Issues

Make sure the Nest thermostat has a strong Wi-Fi signal and can connect to the internet. 

If your thermostat can't detect the Wi-Fi network, try repositioning the router, getting rid of any obstacles, or connecting your thermostat via a mobile hotspot.

5. Reset the Nest thermostat

If you can access the thermostat menu, you can try resetting the Nest thermostat to factory defaults. This can help clear out the flashing blue light and return it to normal condition. 

However, before going through with a factory reset, don't forget to delete the device from the Nest and Google Home apps. 

To factory reset your Nest thermostat:

  1. Open up the quick view menu on your thermostat
  2. After that scroll to settings and tap the ring button to enter
  3. Then turn the ring until you get to the “Reset” option and enter into that menu
  4. Cycle to “All Settings” and tap on the ring button
  5. Follow the instructions to confirm your changes
  6. Wait for the device to reset. Usually, it’s followed by a quick restart.

Last Resort: Replace the Thermostat Or Get Help From a Professional

If all the above steps won't solve the issue, then your only option is to get it looked at by a professional or replace it entirely. 

In this section, let's take a look at troubleshooting a Nest Heat Link that's flashing blue. 

Please note that these steps are geared towards the Heat links for the Nest Thermostat E and 3rd generation learning thermostat but you can also troubleshoot this for 2nd gen, it's just the indicator colors will be different.

1. Wait 5-10 minutes

Most of the time, the flashing blue light on a Nest Heat Link (E and 2nd Gen) will imply that it's updating, in pairing mode, or trying to connect to the thermostat. 

So if you have a Heat Link that's directly connected to your thermostat wiring in place of the Nest Thermostat E, it might be trying to connect to the thermostat or the Nest app. 

Besides that, it might also be updating the firmware (indicated by a rapid blinking pattern). In whatever circumstance, make sure to wait it out for five to ten minutes before proceeding.

2. Check the Thermostat for Any Error Messages

If the blue light keeps flashing for more than five minutes, check the Nest thermostat or Nest app for any error messages. 

Usually, the thermostat will show the H71 error message along with instructions on how to fix it.

Simply follow the instructions to re-pair the thermostat with the heat link by restarting the connection or improving the signal strength between the two devices.

To check if the Heat Link is malfunctioning, try pressing the buttons on the heat link to see if you can operate it manually. 

If the hot water or heating indicator lights or patterns show up, with the necessary equipment kicking in, then it's most likely a networking issue and not a hardware defect. 

That said, if you can't get the Heat Link to operate manually, try checking the wiring connections or getting help from an expert. 

If the Heat Link can be operated manually, but still can't connect to the thermostat or mobile app, try restarting the device. 

  1. To restart, press and hold the center button on the Heat Link for 8 seconds (10 seconds if you have a 2nd or 3rd gen Heat Link) and release it. 
  2. The Heat Link will start pulsing blue (slowly) during the restart process. 
  3. Give it several minutes to fully restart and see if the blue flashing light goes away. 
  4. If you have a learning thermostat, the indicators will light up in green or yellow during the restart process. 

After a successful restart, make sure the Heat Link works manually, and then try to reconnect with the app or thermostat. Usually, the Heat Link will reconnect automatically.

Nest Heat Link
Restarting the Heat Link usually does the trick

5. Improve Signal Strength for the Thread Network

Maybe your Heat Link works manually but struggles to maintain a connection with the thermostat or the Nest app. 

If that's the case, you can try to reconnect the device or improve the signal strength for the thread network. 

While doing so: 

  • Make sure the maximum distance between the Heat Link and thermostat/thread router device is no more than 20-30 meters (65-100ft). 
  • Beyond that, you can try to bridge the gap with the help of several Full Thread Devices such as Thread-compatible light bulbs and electrical plugs. 
  • If possible, try to maintain a direct path, free of obstructions between the thermostat and your heat link, this can help improve the signal and prevent the heat link from constantly disconnecting from the network.
  • Check the settings of your Wi-Fi router and make sure it has data and can connect to the internet

Also, if you haven't already, make sure to install a C-wire to your thermostat so it has more stable power coming in and can permanently maintain its Thread radio. 

If the Heat Link continues flashing blue after trying out the steps I’ve laid above, it might be time to consider a factory reset to eliminate glitches.

However, don’t forget that this will erase all settings and restore them to default, including your connectivity settings.

Also, before performing a factory reset, be sure to remove the device from the Nest app.

To delete your Nest thermostat and Heat Link connection from your Nest app, before you factory reset the thermostat: 

  1. Open and sign in to the Nest app on your device.
  2. If you have multiple homes, tap the downward-pointing arrow in the top-left corner to select the home with the device you want to remove.
  3. Once you’ve picked the correct home, and you’re on its “Home Screen,” tap on the settings icon (gear symbol).
  4. Then, tap on the Nest thermostat you want to remove.
  5. Scroll down and select the option “Remove Nest Thermostat”
  6. Follow the in-app instructions to provide any confirmations
  7. After that, the Heat Link will be deleted from the Nest App.

To manually reset the Heat Link:

  1. Press and hold the Heat Link's center button for 20 seconds, until its status light turns solid yellow, then release it.
  2. The reset process will begin. Wait a couple of minutes or until the status light pulses blue to finalize the reset process.
  3. After a successful reset, you must add the Heat Link back into the app. 
  4. To do so, first, remove its cover or front plate
  5. This will reveal the QR code located on the battery compartment.
  6. With this in hand, access the settings within the Nest app and select “Add product.”
  7. Follow the on-screen instructions to scan the QR code and add the Heat Link back to the app.
  8. When prompted, inform the app that your Heat Link is already installed, which will allow you to bypass the installation instructions.

If all of the above steps can't seem to get rid of the dreaded blue flashing light, then you can either keep controlling the heat link manually or consider getting help from a professional to repair or replace it. 

Wrapping Up

A flashing blue light on your Nest thermostat or Heat Link almost always implies a network issue. However, when troubleshooting, you might even have to perform resets or check the wiring strip.

So make sure to take a look at the guides I’ve mentioned above and drop a comment if you have any questions.


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