Nest on combi boiler vaillant ecotec pro 28

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Hi all,

I want to buy nest 3rd generation and install myself on my boiler but when I look at the wiring on nest instructions I can see that there are 2 ways to do so. One is 230v and one is dry contact.
i have attached a picture of my motherboard.
I have to wire L & N from 230V to N & L to the heat link so far nothing difficult. Then, my question is I should wire from 230V rt one line to n’ 3 on heat link and loop n’2 to L and wire the earth from 230V to the earth next to T1 & T2 and remove that loop on 24V tt or I have to wire N & L as the previous but instead using 24V rt wire in 2 and 3 on heat link?
What the difference between them ? if they both correct .
Hopefully everything is clear...
0F642B73-40C6-447D-8FE8-5534531758B3.jpeg

Thanks​
 
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Although it says bus, that does not mean it is opentherm, I think opentherm is around 40 volt, but I would want to see opentherm written in the installation instructions before connecting up, and I would use separate cables for the low and extra low voltage.

The on/off function of Nest is volt free, does not matter if 24 (extra low voltage) or 230 (low voltage) however clearly not as good as opentherm if that can be used. It seems some boilers you remove a link when using opentherm, but you need to read the installation instructions you can't guess, you have to read what it says.
 
@ericmark the op hasn’t mentioned opentherm.

@Maurizio - not much of it makes sense, and you have removed the cover from a boiler that forms part of the combustion circuit, so I do hope you intend on carrying out 26.9 critical safety checks after work on a gas appliance.
 

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