Help with wiring my Worcester 26si to nest.

[Churchies49]

Hi guys.
I've looked at loads of threads but I'm wondering how to install my nest 3rd gen.
I'm thinking I need to wire 4 wires?

Ns - N
LS - L
LR -3

And L to 3 ???

And also will I need to disable my programme box?
Thanks guys

 

[stem]

You're almost there. As you have figured:

Ns (Neutral supply) = Nest N
Ls (Live supply) = Nest L
Lr (Live return) = Nest 3 Heating call for Heat

But you will also need to add a wire to link Nest terminal 2 Heating common, to the Nest terminal L

The Heat Link should also have an earth connection as per the Nest instructions if using T1 & T2 to power the remote thermostat.

Any existing externally wired thermostat / programmer should be disconnected and removed completely, otherwise it will interfere with the operation of the Nest.

If you have to open up a room sealed compartment of the boiler to access the wiring terminals (This is not the case with all boilers, with some you do & some you don't) then it should only be done by a RGI (Gas Safe Engineer) who can make the appropriate checks to make sure that it is sealed up again properly afterwards.

Edit
Wiring diagram added