Replacing Honeywell T40 with Nest thermostat

[notinventedhere]

I've read a bunch of other threads but I'm still not 100% sure I know how to wire up the Nest Heat Link correctly and obviously don't want to blow up my £179 shiny new gadget!

The Honeywell T40 has 3 wires coming in which as far as I am aware correspond to:
1 - [live]
2 - [neutral]
3 - [switched live]

The Nest heat link requires these connections:
Live connected to "L"
Live connected to "2 [common]"
Neutral connected to "N"
Switched Live connected to "3 [call-for-heat]"
[see pages 32 & 34 of installation manual: https://s3.amazonaws.com/support-as...ges/Nest-Thermostat-Installation-Guide-UK.pdf]

So does that mean the corresponding wiring should go:
[code:1]Wire *was* here in Honeywell -------- Wired *now* to here in Nest heat link
1 [live] ---------------------------- 2 [common] with jumper cable to L, as specified in Nest manual
2 [neutral] ------------------------- N
3 [switched live] ------------------- 3[/code:1]

Thanks in advance for any help you can give me!

 

[stem]

You have worked it out correctly.

For the Heatlink, you will need to link terminals L and 2 (Common) and also connect the Live supply to one of them.

3 (call for heat) is the switched live

N is of course, Neutral

And somehow you will need to power the thermostat, either using the plug in power supply, or by wiring it to T1 & T2 at the heatlink

 

[notinventedhere]

Awesome, thanks.

Yes there's no existing wiring that I can power the thermostat with. If I can figure out the correct type of wire to buy I'll wire the thermostat to the heat link, otherwise there's a nearby power socket I can use with the USB power supply.

 

[notinventedhere]

Ah, seems a few people have asked the same question about what sort of wire to use for the T1/T2 thermostat power connections, and the consensus seems to be that "speaker wire" or "bell wire" does the job.

 

[notinventedhere]

For any future readers, I wired up the Nest at the weekend using the method specified in my post and it all works fine. I used this 24/0.2mm "equipment wire":
http://www.maplin.co.uk/p/maplin-equipment-wire-24-02mm-white-10m-ba41u
from Maplins for both the jumper connection and the T1/T2 12V power to the thermostat.

 

[muggles]

An alternative would have been to use the wires in the T40 for your T1 & T2 wires, and put the Heat Link at the other end of the old T40 wires where it's out of sight....