Nest install / wiring question

27 Jan 2017
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United Kingdom
I’m looking to self install a Nest Learning Thermostat on my Worcester Bosch 280 boiler.
The wiring looks straight forward, but I just wanted to sense check before I go ahead.
The boiler doesn’t have a stat currently, so on the stat section has an unused N connection.
1 & 2 are jumpered (2 shows 240v, 1 is 0v), a 3 is unsued and unmarked, and 4 is unused and marked Frost Stat.

So I assume I can run a 4 core to the Nest Heatlink, and wire up as follows :-

N from boiler to N on heatlink

2 (240v Live) from boiler to L on heatlink, and then jumper L on the heatlink to common / 2(do I need to run a 3A inline fuse or not? On the jumper cable)

1 from boiler to 3 (relay open) on the Heatlink

Earth (needed or not? As Nest stat will be wireless)

Is that pretty much it, bar testing, tidying, and testing again?
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Hi Stem. The manual has numbering backwards to what i wrote but is the same setup. So if we work off the diagram, 1 & 2 are for frost stat so not used. 3 runs 230v when boiler is on. 2 runs 0v but is jumpered between 2 and 3 normally (as there is currently no room stat).

Also looking at the boiler again, the mains feed is easy to tap off too. So realistically should I run Live and Neutral from the mains terminals, then run 2 from the Heatlink to 3 on the combi, and finally 3 on the heat link to 4 on the combi.

Also, as I haven't seen that diagram before, what does the zig zag line between 2(N) and 3 mean on the hopewell stat? Do i need to connect something form the heat link into N?
I'm still not quite sure what you mean about it being in reverse, so I can only advise based on the wiring example of terminals 1 to 5 in the manual as copied below, which you say is in reverse to yours, so you will need to convert it.


Boiler terminal 5 is the neutral = Nest neutral
Boiler terminal 3 is the live = Nest live
Boiler terminal 4 is the switched live = Nest 3 (call for heat)

You will also have to link the Nest live terminal to Nest 2 (common) terminal

Remove the link between the boiler terminals 4 & 3

Ignore the Honeywell stat wiring details, the zig zag is something inside the stat and doesn't apply to Nest.

Don't proceed if in any doubt at all. If you can post a photo of your boiler terminals or the wiring diagram from your boilers manual it will allow a positive confirmation.
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