Nest 3rd generation help required

2 Dec 2016
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United Kingdom
I posted this in the central heating and plumbing forum but someone suggested I post here. I am new to this site so please be gentle!

I have just purchased a 3rd generation Nest and need to install to the following set up:
• Vaillant ecoTech Plus 428 boiler
• Drayton LP522 Programmer (pic 1)
• Drayton wired room thermostat (pic 2)
• hot water tank in airing cupboard upstairs.

I don’t appear to have many wires to swap over to the Heat Link, but am not sure which wiring diagram to use from the Nest manual. I also can't see how the existing thermostat in the hallway links to the boiler (the supply to the thermostat also looks like it may be 230v - so I may have to use the usb power?). The thermostat is quite far away (2 rooms in between) from the existing boiler.

My wife and I would be very grateful of help with the wiring! many thanks in advance, Rick.
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Your installation is fairly simple, there are three specific steps.

First of all you need to remove the existing wired thermostat from the wall, and terminate the wires in a junction box as follows: The 2 wires from the neutral terminal should be connected together (as they are now) and, then the 'L' wire (brown) and 'Call' wire (terminal 3, Blue with Brown sleeve) should be connected together.

Alternatively, if you want a neater job without the junction box, you could trace the wires back to their origins and rewire accordingly so as to achieve the same thing. Depending upon the method used by the original installer this could simply involve putting some links in a junction box, or it may need you to run a new cable. This would be a more professional /neater method because the redundant thermostat cables can then be removed and you won't have a junction box on show. But you do need a reasonable level of electrical competence to do this.

Second. The programmer needs to be removed, and replaced with the Nest Heatlink. But note first which wires go where. Then:

The Live wire (Brown) from the old programmer needs to go to the Nest Live terminal (L)

The Neutral wire (Blue) from the old programmer needs to go to the Nest Neutral terminal (N)

Link the Nest Live terminal to the heating and hot water 'commons' terminal 2, and terminal 5

The Black wire presently in terminal 3 (hw on) goes to the Nest terminal 6 Hot water 'Call for Heat'

The Black wire presently in terminal 4 (ch on) goes to the Nest terminal 3 Heating 'Call for Heat'

Finally the Nest thermostat needs a 12V power supply. This can be done by wiring it to the Heatlink terminals T1 & T2 or using a separate 'plug in' power supply.
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Awesome, thanks for the detailed reply, will give that a go. Many thanks, Rick

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