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Usually, a flashing yellow light on your Nest thermostat and Heat Link modules suggests an issue with their connectivity.

In that case, it’s best to bring the thermostat closer to the Heat Link and restart your devices.

However, if that doesn’t solve the issue, you might have to troubleshoot further, so let’s dig deeper.

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.

Why Your Nest Thermostat Starts Flashing Yellow

When a Nest thermostat or Heat Link starts flashing yellow, it usually indicates a connection error between the Heat Link and the Google Nest thermostat.

In such cases, the Heat Link's status light changes to yellow, preventing the thermostat from controlling your heating system until the connection is re-established.

On the thermostat, a red circle displaying an error code might appear, alongside a message indicating that it can’t connect to the Heat Link.

Compatible Models

This guide focuses on the European Google Nest thermostats. This includes:

  • Nest Thermostat E 
  • Nest Learning Thermostat 3rd Generation
  • Nest Learning Thermostat 2nd Generation
  • And their corresponding Heat Link devices

Nest Thermostat E

Smart Thermostat with Heat Link

Nest Thermostat E and Heat Link

If your Nest Thermostat E’s Heat Link has a blinking yellow light, either on its own or when you press the status button, it’s meant to notify you of important alerts. 

This is almost always related to connectivity issues between your Heat Link and Nest Thermostat E but in any case, you need to take a look at your thermostat display or the Nest app for any error codes or messages.

If the alert mentions that the Nest Thermostat has lost its connection with the Heat Link, you can try to see if the Heat Link operates the heating system manually before troubleshooting the issue. 

To control the Heat Link (for the Nest Thermostat E) manually, double-press the status button and wait for the indicator lights to turn green. 

After this, you can try troubleshooting the issue further without having to worry about the heating. 

If you have a programmer still installed (and configured to “Always Heat”), you can also use that until you fix the issue with your Heat Link.

Heating Equipment
You can control the Heat Link or heating programmer manually for a quick fix

3rd Generation Nest Learning Thermostat

Intelligent thermostat with Heat Link

Nest Thermostat 3rd Gen PLus Heat Link

In these models, a steady yellow light directly indicates that the Heat Link is disconnected.

So as mentioned above, make sure to manually turn on the Heat Link until you resolve the issue. You can do this by pressing the status button until the heating and hot water indicators light up in green.

Meanwhile, the status indicator will remain yellow.

2nd Generation Nest Learning Thermostat

Intelligent Thermostat with Heat Link

2nd Generation Nest thermostat plus heat link

For the 2nd Gen Heat Link, there can be three separate instances where you would encounter a yellow light:

  • Solid Yellow (without flashing): The Heat Link is disconnected from the thermostat and the heating equipment is turned off
  • Blinking Yellow: The Heat Link is disconnected but the heating equipment was turned on manually
  • Alternating between green and yellow: The Heat Link is in pairing mode and trying to connect to a Nest Thermostat 

As you can see, the yellow light on your Heat Link is always trying to indicate a connection error with the Nest thermostat. 

So until you restore the connection, it’s a good idea to manually control the Heat Link.

To turn on the heating manually, simply press the button twice for Nest Thermostat E or once for the 3rd and 2nd gen Nest Learning Thermostat.

Turning off the heating equipment follows the same pattern.


However, don’t forget that manual heat mode means your home will continue to be heated until you manually turn it off, even if your thermostat reconnects.

This also applies to your hot water system, if it’s also configured to your Heat Link.

On top of that, your system won't follow your regular schedule or other thermostat settings while in manual heating mode, such as OpenTherm boiler modulation of water temperature.

So make sure to constantly monitor the situation or get help from a professional if you’re unsure of the troubleshooting process.

Heating equipment 2
Manually controlling the heating equipment can be tedious so make sure to troubleshoot the issue as fast as possible

After switching your Heat Link to run manually, you can start troubleshooting the issue.

Step 1. Check the Nest App or Thermostat for any Indicators or Alert Messages

In the case of the yellow flashing light, it’s almost always when the Nest Thermostat loses the connection to the Heat Link.

This can be due to several reasons, with the most probable being a weak Thread connection.

So the first thing you should do is to check your thermostat or Nest App for any alerts. They will provide instructions and prompts to help you reconnect with the Heat Link.

However, if your thermostat doesn’t show any alerts and cannot control the Heat Link remotely, it’s time to move on to the next step.

As long as your Heat Link is not too far away from your thermostat, a simple restart may fix the issue.

To force-restart your Heat Link:

  1. Press and hold the Heat Link’s status/center button for about ten seconds. Or until the indicator lights turn off.
  2. After that, let go of the button and wait for it to restart
  3. Wait a couple of minutes until the Heat Link powers up. Usually, the status light will turn green to indicate a successful connection. 
  4. However, if it turns yellow again, you’ll have to troubleshoot the issue further.
Nest Heat Link
Restarting the Heat Link has a higher chance of resolving any connectivity issues

Step 3: Reposition Your Devices and Test the Connection

Even though it has wider coverage than regular Wi-Fi or mesh networks, the Thread can also run into obstructions and signal losses. 

To make sure this isn’t the issue, you can try moving the thermostat closer to the Heat Link and trying to re-establish a connection. 

This is pretty straightforward if your Nest thermostat runs on batteries.

So if you can remove the thermostat from the stand or wall mount and bring it closer to the Heat Link, at least until it can complete the connection, this would help create a more stable connection. 

Also, make sure your Heat Link isn’t hidden away behind the boiler or heating equipment. If so, reinstall the Heat Link so it’s about a couple of feet away from your heating equipment with enough room for its radio to pick up a strong signal. 

Repositioning the Heat Link may require some electrical DIY so make sure to follow the necessary safety precautions or get help from a professional.

Test the Connection

After bringing the devices closer and minimizing any signal losses or obstructions, you can check the connection strength between the thermostat and the Heat Link. To do so:

  1. Open the settings on your Nest thermostat
  2. Head over to “Equipment”
  3. Select “Heat Link” 
  4. Tap on “Test”

This will try to re-establish a connection with the Heat Link. Usually, this will help resolve the issue provided the devices are closer to each other. 

However, if the test fails, you might have to improve the connection and try again, reset the device, or get help from a professional.

Tips for Maintaining A Secure Connection

To maintain a secure connection between your Nest Thermostat and Heat Link:

  • Try to reposition the Nest thermostat so it's closer to the Heat Link (with a maximum distance of 30m)
  • Keep the thermostat closer to the Heat Link during the pairing process
  • Use additional Thread routers or Full Thread Devices to improve signal
  • Clear out any obstructions between the Nest Thermostat and Heat Link
  • Reinstall the Heat Link so it’s not hidden away behind large equipment or walls
  • Try getting rid of unnecessary 2.4GHz Wi-Fi networking devices such as other smart devices and routers that may be causing interference
Wi Fi Router
Providing sufficient signal strength to your Heat Link will help prevent connectivity issues in the future

Before calling in the professionals, you can pull up one final trick by resetting the Heat Link to factory defaults. 

However, before doing so, make sure to delete your Heat Link connection from the Nest or Google Home apps.

To reset the Heat Link: 

  1. Simply hold down the button for a solid 20 seconds (instead of the regular 8 seconds for a restart). 
  2. After that, wait for the device to restart
  3. Then, add the Heat Link to the Nest app using the QR code or pairing code inside the Heat Link’s battery cover 
  4. Also, don’t forget to pick the “already installed” option in the Nest app so you can skip through the physical installation instructions.

However, if you can’t fix the issue after a factory reset, it might be time to call for help from a professional.


The flashing yellow light on a Heat Link usually implies that the Nest thermostat has lost its connection with the Heat Link. 

You can easily fix this with a simple restart, but other than that, improving the Thread signal and resetting the Heat Link might also help. 

So try these steps out yourself or get help from a professional if you run into any major issues.


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