I have a Nest Thermostat E, which requires me to replace my thermostat with the Nest Heatlink.

Google provides step by step instructions on how to do this using a series of questions and answers. However, I'm struggling with a lack of knowledge.

Does your diagram have any of these labels for the common wire?

  • COM
  • Common
  • HCOM
  • No exact match

-> No exact match

Does your diagram have any of these labels for the normally open wire?

  • NO
  • NA
  • CALL
  • H ON
  • Demand
  • Call of heat
  • N/O
  • On
  • No exact match

-> No exact match

The common wire is always connected to one end of your switch...

I identified the brown wire (1) as the Common wire.

When your heating is off, the "normally open" wire is the one that isn't connected to your switch

By my admittedly very limited understanding of this description, this could either be the Grey wire (2) or the Black wire (3)?

The instructions then go on to say wire the Common, and Normally open wires into the Heatlink E, and disconnect all of the others and cap them off.

So at this point i'm left with some questions I'm hoping someone here could please answer for me:

  • Exactly which wire I should use as the 'normally open' wire?

  • I recognise the Yellow/Green as earth/ground. Should this really be capped off and not connected?

  • I like to learn rather than just do, so an explanation on why it may be laid out like it is (Wire's 2 and 3 leading to the same switch).

Here are pictures of the current wiring and the diagram.

Thermostat Wiring

Thermostat diagram



Google seems to be truly unhelpful on this one of their products.

Your existing thermostat has a live feed in at terminal 1, which is brown (as it should be) and the neutral is connected to terminal 2 (it should be blue, and is sleeved to indicate so), that is likely there for a function light. The switched output is at terminal 3, looks like that's a black wire.

So you need the brown to the C terminal and the black to NO.

Here's the only image I could find, from here

enter image description here

The E version is battery operated, so doesn't use any mains power. No ground connection or neutral are needed to the Heat Link, so those wires should be insulated and not connected.

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  • \$\begingroup\$ This appears to be for the Nest Thermostat and Heat link. Not the Nest Thermostat E. I believe the Heat Link in the Nest Thermostat and the Heat Link in the Nest Thermostat E are different. \$\endgroup\$ – Leigh Bicknell Dec 3 '19 at 17:20
  • 1
    \$\begingroup\$ @LeighBicknell You're right, I'd assumed they were the same. I've updated it with what little I can find about the E. \$\endgroup\$ – Phil G Dec 3 '19 at 18:22
  • \$\begingroup\$ Hi, I have wired it up like this and the boiler is coming on when my nest tells it to, but the radiators aren't heating up fully like they did before. It's like they're only getting half as warm, as if the pump isn't running or something. Looking at the diagram, is it possible that the sleeved blue wire is connected to the pump? \$\endgroup\$ – Leigh Bicknell Dec 6 '19 at 10:15
  • 1
    \$\begingroup\$ Per the guide for your existing thermostat, the neutral connection supplies a heating resistor that is used to compensate for the heat generated by the switched contacts themselves when the load is lower, so it shouldn't be doing anything useful in your system. heatingcontrols.honeywellhome.com/Documents/Installation-Guide/… Is the pump running? \$\endgroup\$ – Phil G Dec 6 '19 at 14:14
  • \$\begingroup\$ I believe Ihe pump is running, all of the radiators are heating up, just not as hot as before. \$\endgroup\$ – Leigh Bicknell Dec 7 '19 at 17:26

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