Upgrading Nest Learning Thermostat: 2nd Gen to 3rd Gen

[Denali]

(I'm in the UK and have a Combi boiler)

Hi, ok, so after 9 years my Nest Learning Thermostat 2nd Generation has failed.  The Thermostat (wall mounted) shows the H2 error, that the Thermostat is not receiving power.  Nothing has changed in my set up, no recent power cuts, etc.  Just came up with this message.  

I took the Thermostat off the wall and charged it via USB, and I factory reset the Heatlink, but no good.  The Heatlink now blinks yellow / green (searching for Thermostat) while the Thermostat after USB charging briefly searches for the Heatlink but then dies.

So I think it's dead!  But 9 years use without issue, not so bad.

So i've bought a Nest Learning Thermostat 3rd Generation, that i'm going to install.

My questions are

1. Do I just delete now (before starting 3rd gen install) my current 2nd gen from my Nest & Google Home apps, so they're ready to go with the new 3rd gen when its installed, so nothing gets confused?

2. I know I need to physically replace all of the Thermostat, Thermostat Base and the Heatlink (so take off the 2nd Gen parts and fit the 3rd gen parts) .  Is the 3rd gen Heatlink wired the same way as the 2nd gen?  i.e. all I need to do is swap the 3 wires that go from the combi boiler to the 2nd Gen Heatlink into the 3rd Gen Heatlink into the same places? 

Thank you! 

Rob

[AlexD]

Thanks for reaching out to us here @Denali . I am sorry to hear your old device stopped working. It is possible the internal battery is no longer holding a charge. If you do happen to take of the thermostat base from the wall you can try charging the display for 90 minutes, after plugging the micro USB into the thermostat base and putting the display on it to see if it turns on and gives you anything. 

You can leave your old thermostat in the Nest app but if you will no longer be using it as it seems it will not turn on you can delete it in the Nest app and it should also be removed from the Google Home app after. But there shouldn't be any problem if you leave it either. 

The 3rd Generation Heat Link has the same connection as the 2nd Generation, with the addition of a extra set of 3 terminals for hot water control for systems that have a system boiler with a hot water tank. But since you have a Combi system you can ignore those. 

The wiring will be exactly the same on the Heat Link side. The wires from the 2nd Generation will just swap into the identical ones on the 3rd Generation models. You'll put the new base on the wall in place of the old one and connect the wires to it, put the display on and it should all be good to go after the setup. 

[Denali]

Thank you very much for the reply, Alex.  

Very clear and all makes sense.

Thanks,

Rob

[AlexD]

I'm happy I could assist. If you have any other questions or if anything else comes up, make sure to let me know. 

Have an amazing weekend ahead and take care!