Nest 3rd generation inquiry

[xouleles]

Just moved to a new property and braved myself to get a nest 3rd gen thermostat. Previously I did setup tado with an extension unit to control HW on my previous property with the assistance of tado support team so i thought to change over to nest. However i realised their support is not the same as i experienced in the past with tado so I am a bit stuck.

My current property has a boiler glow worm 15r energy installed with drayton LP522 programmer next to the boiler and a honeywell wired thermostat in a different location. The plan is to replace the LP522 with nest heatlink and the honeywell with the nest unit.

Existing wiring diagram of the LP522:


Existing wiring of the honeywell:


From my understanding by reading various similar discussions I may have to "rewire" or modify the connections of the wired central unit where the tank resides. I hope that this is not the case and i will be able to accomplish my plan without this. Is this possible?

Here is the wiring of the wired central unit next to the tank in the airing cabinet:





Could you please advice the wiring arrangements required for the LP522-> Heatlink & Honeywell -> nest display?

Many thanks in advance

 

[stem]

The LP522 wiring terminals are thus:

The existing wires are simply moved from the terminals of the LP522 to the terminals of the Nest Heat link that have the same function. Don't worry about terminal 2 not having a wire in it, very few do. If your system doesn't need it now, you won't need it with the Nest.

So:
LP522 N = Heat link N
LP522 L = Heat link L
LP522 1 HW off = Heat link 4 Hot Water Satisfied
LP522 3 HW on = Heat link 6 Hot Water Call for Heat
LP522 4 CH on = Heat link 3 Heating Call for Heat

The Heat link common terminals (2 & 5) need to be wired with links to the Heat link L terminal

The Nest thermostat can be powered by wiring it to Heat link T1 & T2 terminals, or alternatively by using a separate plug in 12V power supply for it.

The existing wired room thermostat can't simply be disconnected as this would leave the heating wiring 'open circuit' and it would not operate. So you can:

1. Leave the existing room thermostat in place and set it to its maximum setting and leave it there, this will prevent it overriding the Nest. Or,

2. Find the origin of the thermostat cable. Note where the wires are connected and disconnect the cable. Then link the terminals where the two ‘live’ switching wires came from together. (This will probably be in the wiring centre) The Neutral, is simply disconnected. Or,

3. Remove the existing thermostat and replace it with a junction box, connect the two ‘live’ switching wires together and isolate the neutral. Or,

4. Leave the existing room thermostat in place and join the ‘live’ switching wires together in a separate connector that you can tuck away in the corner of it.

Your existing thermostat looks like a T6360B if it is, the live switching wires are connected to terminals [1] and [3] as can be seen from the diagram below. This diagram should also be printed inside the thermostat.

Check the thermostat carefully though, because if it is a T6360B different wiring colours to the norm have been used for wiring yours up. Normally red and yellow are used for the live wires that go to terminals [1] and [3], yours uses red and blue instead. But it will work provided they are also transposed at the other end of the cable.