Wiring Nest Thermostat E Heatlink in place of original Thermostat

Question

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.

Thanks

Answer 1

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

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.

Answer 2

"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."

Can confirm this works for me - ignore the image colours!