Quick nest removal question

[Rn87]

I went to remove my old nest today which was installed when we had a combi boiler fitted and I had a quick question.

I want to take the heatlink out and replace with a simple honeywell T630B
but i noticed instead of a jumper on the live to the common there's a second live coming from the boiler to the common instead?

https://imgur.com/a/ksLHw

L from heatlink to 4
N from heatlink to 2
Call for heat to 3

what do i do with the extra wire?

 

[Echo the husky]

Your wiring conversion is incorrect.
The 2 core cable form the boiler might be extra low voltage, (you haven't said what boiler you have) if it is the Honeywell stat isn't really suitable, it won't be very accurate. You would need a 2 wire thermostat, one with voltage free terminals. Switching mains into extra low voltage boiler inputs will destroy the boiler PCB.

 

[Rn87]

The Boiler is a Worcester bosch green star 25i.

 

[Echo the husky]

The nest should have been been wired so power was taken from the boilers thermostat terminals, and should have been connected with the coloured insulation contained within the nest enclosure, but anyway. A programmable room stat or external programmer is normally used unless the boiler has the optional programmer module fitted. (unlikely as Nest is a programmable roomstat)
See diagram for thermostat connection:

 

[Rn87]

Thank you Echo. didn't notice the 4th terminal was called terminal 1 on the t6360 when i typed this post.

Thanks again!

 

[Echo the husky]

Just to be clear my terminals are not shown in the honeywell layout, but the wires to the terminal numbers are correct.