Nest 3rd Generation wiring.

[Airiasas]

Hello everyone,

I have a Worcester Greenstart 24i Junior combi boiler installed in my house.
I'd like to wire a nest 3rd gen thermostat.
The programmer wiring:

The thermostat dial wiring (RTS1):

It looks like the fused switch is wired in a programmer unit:

So switching off fused switch cuts off power to programer and combi boiler.
My question would be how to wire the nest heatlink? Seems that there are too many wires in this programmer or is this normal? Thank you.

 

[stem]

That's a perfectly normal installation. At the moment, you have separate controllers for time and temperature of your heating, Nest combines the two functions into a single unit. Usually the Nest Heat link is installed in the place of the programmer. All of the existing wires from the current programmer are moved to the Heat link terminals that have exactly the same function. You should have the wiring diagrams for the existing programmer and Nest and so as to be able to work it out.

The existing thermostat can be left in situ and set to maximum so that it doesn't interfere with the operation of the Nest, or if you want to remove the old (RTS1) thermostat completely then:

1. Trace the thermostat cable back to its origin.

2. Take take a photo, or make a note of where the live switching wires (the brown wire and grey wire with brown sleeve) are connected at their origin.

3. You can now disconnect all of the wires going to the old thermostat including the neutral and earth and remove the cable and old thermostat.

4. Insert a wire link between the terminals where the two live switching wires (the brown wire and grey wire with brown sleeve) have just been removed from, so that they are now electrically joined together.

 

[Airiasas]

I am going to wire the nest thermostat to T1 & T2.
Boiler connections:
LR: Grey
N: Black
L: Brown
Ground: Green and yellow

What would be nest Heatlink connections:
N: Blue (coming from the fused switch)
L: Brown (coming from the fused switch) and Brown (coming from the boiler)?
1: Nothing?
2: Grey(coming from the boiler LR)?
3: Black (coming from the boiler)?
4: Nothing?
5: Nothing?
6: Nothing?
OT1: -
OT2: -
Ground: Green and yellow (from the fused switch) and Green and yellow (from the boiler)?
T1: Nest thermostat T1
T2: Nest thermostat T2

Basically, the way it's set up nest heat link would be in the middle between the fused switch and the boiler? That's what confuses me.

And that's the diagram from the controller:

Many Thanks.

 

[stem]

Basically, the way it's set up nest heat link would be in the middle between the fused switch and the boiler? That's what confuses me.

It's just being used as a junction box, L N & E in from the FCU and L N & E out to the boiler, just keep the wires connected as they are.

Whenever there are two items wired to the same fused switch, then unless they are both wired directly to the fused switch, one will be a junction box for the other. It matters not which one it is.

Fused switch.....>Heat Link......>Boiler

Or

Fused switch.....>Boiler......>Heat link

3: Black (coming from the boiler)?

Probably not a good idea to connect a black wire currently in the Neutral terminal of the programmer to Terminal 3 of the Heat link which is a live connection!

Here's a diagram for you. Easier to understand than my waffle. No need to touch the wiring at the boiler end and the old thermostat cable can be removed once disconnected.

 

[Airiasas]

And finally just to check both ground wires Green and yellow (from the fused switch) and Green and yellow (from the boiler) go to the same Earth connection in the Nest heatlink? Thank you.

 

[stem]

Actually the Nest instructions say that the earth at the Heat link itself is only necessary if you connect the T1 & T2 terminals to the Nest Thermostat T1 & T2. However for earth continuity, the earth wires from the fused switch and the boiler must remain connected together. Once the room thermostat cable with earth wire will have gone, you should be able to get the remaining two into the Heat link earth terminal.

As they are stranded wires, be careful that there aren't any stray whiskers of copper poking out from the terminal which could touch another terminal. Heat link terminals are quite small and close together.