Thermostat And Boiler Not Communicating [SOLVED]

Boilers are essential for heating your home, especially in winter and the last thing you want to do is come back home only to discover that your boiler is not responding to the thermostat adjustments you are making. 

While this can be frustrating for homeowners, a few things can stop your thermostat and your boiler from communicating, but the good news is, that there is always something you can do to fix the problem.

When a thermostat and boiler seem not to be communicating, this is likely due to a stuck relay switch. To resolve this problem. You’ll need to reset your thermostat to release the relay switch and will reconnect your thermostat to a boiler.

How do you reconnect a thermostat to a boiler?

To reconnect your thermostat to a boiler so that communication is restored, you’ll need to reset the thermostat or a boiler’s receiver unit. 

The receiver unit or the heat link is a part of a thermostat that receives and relays signals from the thermostat to the boiler. A thermostat or heat link reset  should release the stuck relay switch and will most likely fix the ‘no communication problem.’

Depending on the make and model of the thermostat you have, refer to the user manual provided by your manufacturer on how to reset the receiver box. (Small device that links the boiler to the thermostat)

However, note that when you reset the heat links or the receiver box, you will erase all program settings on your thermostat, and you’ll need to start afresh to reprogram.

Reasons Why A Thermostat and Boiler Won’t Communicate

A thermostat and a boiler not communicating could mean a few things. Let’s dive right into how we can troubleshoot each of these problems.

1)      Boiler not turned on

While this is a no-brainer, you’d be surprised how often this problem is among homeowners. A boiler that is not turned on will not respond to a thermostat.  You could be saying to yourself, ‘but I never turned off the boiler’ well, there could be another member of your family that turned off.

Not only that but there are also other things that could cause your boiler to turn off. For example, when a sudden power surge occurs, the circuit breaker can trip and cut power to your boiler.

The fix.

Check if the boiler is on. If the switch is in the on position, but there is no sign of power, look at the electrical circuit breaker box switch. Look out for any tripped switches.

Reset a tripped switch if there is any. Although this can sometimes solve the problem, if the switch trips again, do not try to reset it; instead, try calling an electrician or a professional because that indicates another issue with electricity somewhere.

2)      Stuck relay valve

When everything is powered up and running (both the boiler and the thermostat) a stuck relay valve from the heat link could prevent the boiler from responding to temperature adjustments on a thermostat. To fix this issue, a restart or a factory reset is required.

3)      Thermostat low batteries

This is a common but often overlooked problem.  These days, many smartphones can be plugged into a home’s power supply socket to be powered up. For these, you’ll never run into low battery issues. But if your thermostat relies on batteries, low batteries could be why your boiler is not responding.

Most thermostats can notify you when batteries are about to die about 1-2 months before they completely die out.

 But if you miss the battery warning message, you can always replace your old dead batteries with new ones.

The wireless signal will be too weak when batteries are weak to communicate with the boiler’s receiver box. Other signs of a low battery may include a faint display on the thermostat’s digital display.

Other times when batteries are dying, the screen will completely go blank.

The fix

The simple fix to this problem is to get new batteries. Replace old batteries with new ones and try using the thermostat again.

How do you know if the thermostat is not working in a boiler?

A few signs can tell you whether or not the thermostat is not working in a boiler. These include the following:

1.       When adjusting the temperature on the thermostat, you should generally notice changes in the temperature. But when the thermostat is not working, there are usually no temperature changes in the boiler.

 For example, if you set the temperature to 68 degrees, leave and return to a home that is 77 degrees. That’s a good sign of a thermostat issue.

2.      Another sign is when the boiler is not turning on when you turn on the thermostat and doesn’t turn off when you try to turn it off using the thermostat.

 In short, a boiler with a thermostat that is not working rarely responds to any thermostat adjustments.

Reconnect Nest Thermostat to a Boiler

Are you using any of the Nest smart thermostats? Here are the steps on how to reconnect a thermostat to a boiler. This is achieved by resetting the heat link(boilers receiver box) to restart or reset your thermostat to factory default settings.

How To Reset a thermostat on a boiler?

TIP: Because resetting the thermostat involves reconfiguring your thermostat, try restarting it, and if nothing works, proceed with resetting.

How to restart a nest Heat link

·         Press the nest button (the big button on your heat link) and hold it for at least 10 seconds before releasing it

  • Wait for a few a second to allow the heat link to restart
  • After it restarts, the heat links color will display either yellow or green

1. Green light: If green is displayed, heat links have successfully reconnected to your thermostat and should be working without problems

2. Yellow light: There is no connection between the heat link and the thermostat. An error code is sometimes displayed on your thermostat. You can use this code to refer to the user manual.

How to reset the Nest Heat link to default factory settings:

  • To reset a Nest heat link to factory default settings, you’ll need to remove the heat link for the account on the app. (That is, if you have a Nest E)
  • For other models, press and hold the heat link button for at least 20 seconds until you see the yellow status light. Then release it.
  •  The heat link should reset and connect to your thermostat if you use a 2nd or 3rd-generation E-learning thermostat. If not, your thermostat will ask you for a pairing code, a 6-digit code found at the bottom of your heat link.
  •  Enter this code on your thermostat to connect.

However, if you are using Nest Thermostat E, you will go to the app’s settings and tap on add product. You’ll need to scan the QR code on top of the battery compartment behind the heat link cover.

Thermostat and boiler not communicating: More fixes

1.       Made sure software was up to date: If your thermostat can’t connect to the boiler, you might need to update the thermostat software. To carry out an update, go to the home screen of your thermostat and select settings>version>update.

2.       If you are using a nest thermostat, try deleting and reinstalling the thermostat on the Nest app

3.       Try to position your thermostat near the receive box/ heat link. And there should be no metal barrier between the thermostat and the receiver box to ensure the connection is working

4.       Turning off auto schedule:

On your smart device. To turn off the auto-learning schedule, go to the Nest app and select the nest thermostat. Then go to settings>Auto schedule, tap the switch to turn it off.

On your thermostat, go to settings>nest sense>auto-schedule. That’s it.


To sum it all up, we have seen that when there is no communication between a thermostat and a boiler, the likely cause for this problem is a stuck relay switch on the receiver unit. But always start with checking whether or not the batteries are good. If you rule out low batteries, that’s when you should proceed with the other troubleshooting steps.

However, if you have tried everything in this guide and nothing seems to help, perhaps consider calling local professionals for help. Thanks for reading.

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