Replacing an old nest thermostate and heatlink with a new one

[jackosound]

Hi 

Hopefully, I can explain this. I have one of the first Nest Thermostats, which failed a year ago because of the wifi chip failing. Google would not replace it so I had to buy a whole new system with a thermostat and heatlink. My problem now is the wiring as I am unsure as the old heatlink is marked differently from the new one. Does anyone know how I should wire this? I have 4 wires Brown & Blue / Brown & Blue. The first pair is marked Live and neutral which is ok and then the 2nd pair,  brown is in number 2 and the blue is in number 3. I have photos if needed

[LarisaL]

Hi there, thanks for reaching out! Could you tell me what type of thermostat you have? Do you have the 3rd Gen or the Nest thermostat E? If you have the 3rd Gen, here is the installation guide, but if you have the Nest Thermostat E, I'll leave you an article here.

[jackosound]

I think it is a 3rd generation one.

[jackosound]

So, I am replacing a 3rd generation with the new thermostat E. I have four wires in the 3rd Generation (Live & Neutral and brown in number 2 and a light blue in number 3 and I am confused about where to put the wires in the new one.

[jackosound]

I know this should be simple 🙈

[AlexD]

Thank you for all the information. You can have a look at the Google Nest E installation video here as well to get a better idea of the installation process. 

What you'll need in this case is to move the wire from the terminal with the number 3 in the terminal that's titled NO on the Heat Link for the Google Nest E. If you have a wire straight into terminal 2 you can move that one to the C terminal on the Google Nest E Heat Link. That is the live power terminal and sometimes it's a live high voltage signal straight into it, other times it's a bridge from the L terminal to 2. 

Now I can't say for sure what type of boiler you have at the location but it seems to be a Combi boiler. The wire in terminal 3 will be the call for heat wire that goes from the Heat Link to the boiler and the wire in terminal 2 is the power wire. When you call for heating the relay inside of the Heat Link will bridge a connection between terminal 2 and 3 to pass the power from terminal 2 to 3 and to the boiler triggering the heating. 

The E version uses the same principle. When you call for heat it will bridge terminals C and NO to deliver power from the C terminal to the NO one that goes to the boiler to trigger the heating.

Any other wires you can cap off but if you are not sure on any of the wires you can get in touch with an installer or Nest Pro if needed to advise you on each. 

[jackosound]

Thank you for the swift reply. Does that mean the  L&N are redundant? 

[jackosound]

Is the new thermostat compatible with the 3rd generation heatlink. Could I leave the old heatlink alone and pair the new thermostat?

[AlexD]

Neutral wire would not be used, so definitely can be capped off. Generally in most installations we would see a bridge from the L terminal to terminal 2 to provide live power to the terminal. In that case you would remove the bridge and use the wire from L.

Now you can also use a separate power wire going to terminal 2, or in the case for low voltage Combi boilers a separate low voltage power source. Since that is the wire that powers terminal 2, high voltage or not, it's best to use that one for the C terminal. 

The 3rd Generation Heat Link and the E version are interchangeable. You need the correct Heat Link for each thermostat. 

[jackosound]

Thank you that all makes sense. Now the blue light is not staying on to pair with the thermostat. 

[AlexD]

Just press the button once on the Heat Link to bring up the status light again during the paring process. 

[jackosound]

It's coming up as green and won't pair with the thermostat. I've held the button for 15sec and a blue light comes on and then goes off but will not pair 

[AlexD]

Green status light would indicate it is paired and connected to a thermostat. What do you see on the thermostat display at the moment? 

[jackosound]

Just a rectangle with a house in the middle 

[jackosound]

Thank you for your patience 

[AlexD]

No worries. Try adding the thermostat in the Nest app and go through the process. If it gives you any kind of error message let me know and me or my colleagues can try and look it up to see what we can try. 

[jackosound]

Tried it a few times and no go. The heatlink won't go factory default as the light is still green after I reset it 

[AlexD]

Gotcha, and you don't get any message or code in the Nest app when you try and add it? To try and reset it press the button on it once to bring up the status LED. After press and hold it until the light goes yellow and let go and wait for it to go blue, after it should stay blue. Failing that you can try taking the batteries out of it for a few minutes and trying the reset again. 

[jackosound]

Sorted. I got it reset and all is good. Thank you so much 

[Vladut]

Glad that my colleague was able to help. if you need anything else, please let us know. Have a great day ahead!

[Vladut]

Hi there, just checking in with you. Do you still need help?