Install a Nest Thermostat - S-Plan - Help :-)

[Jord]

Hi All,

It would be great for someone who please share how i can get this up a running.
I'm pretty good with wiring and have installed Nest Hello and my own security alarm system.....but i am absolutely stumped at the Nest Thermostat.

I have watched countless videos on Youtube for the S-plan set up.

I have a UP2 Controller by the boiler which i have attached an image. Located in the utility room. I can easily transfer the wiring over to the Nest receiver and adding in the common wires.

I have a honeywell thermostat in a room located not fair away which has 4 wires - as per the image attached.

The problem i am facing i would like to have the nest thermostat hard wired on the wall and note plugged in:

1). Why are there double wires in the current UP2 receiver? is this coming directly from the room thermostat?

1).Where is the thermostat wires going to? I have a central control wiring box in a spare room cupboard where he water tank is, but none of the wires look like those one there, mainly because i cant see the wider earth cable in there. The heating and water zone valves go into this.

2). I need to wire these to the nest receiver on the ground floor.

Can anyone advice the final steps? I am so close

 

[Jord]

So i need to find a way to remove the current thermostat from the wiring centre or where it is wired to so i provide the nest with 12v.

 

[stem]

From your diagram the UP2 wires are:

N. Neutral
L. Live
1. [Not Used in your case]
2. [Not Used in your case]
3. Hot Water Call for Heat
4. Central Heating Call for Heat

The easiest way to install Nest is to swap the wires over from the UP2 to the Nest receiver, if you want to relocate the Nest receiver, it becomes much more complicated, the existing cables would need to be re-routed or replaced. I normally find it's easier to start again from scratch.

The two wires in N and L are usually the mains supply from the fused connection unit and the mains supply to the boiler. Perfectly normal, but they need to be transferred to the N and L at the Nest exactly as they are.

The existing wires move from these terminals to the Nest terminals that have exactly the same functions.

You also need to link Nest terminals L, 2 & 5 together.

To disconnect the old thermostat and reuse the cable, a minor wiring modification is required, to maintain the integrity of the circuit:

1. Trace the thermostat cable back to its origin.

2. At its origin, take take a photo, or make a note of where the switching wires [Red and Yellow in your case] are connected.

3. Disconnect all of the wires in the cable going to the old thermostat and also remove the old thermostat.

4. Insert a wire link between the terminals where the two switching wires [Red and Yellow in your case] have just been removed from, so that they are now electrically joined together.

5. Once the old thermostat cable has been completely disconnected, if you wish to, you can use two of its wires to connect T1 and T2 at the Heat link to T1 and T2 at the Nest thermostat.

 

[Jord]

thnks so much for the help - extremely helpful.

My main stumbling block is i would like to use the existing wiring for the room thermostat to have the nest thermostat in that room.

any pointers for this? i can provide more images

 

[stem]

Once the old thermostat cable has been disconnected at both ends as per my post above, you can then use it to connect T1 and T2 at the Heat link to T1 and T2 at the Nest thermostat.

I'm guessing that your problem is that whilst the thermostat end is in the right place for the Nest thermostat, the other end will likely be at a wiring centre and not where the Heat link is, so will need extending or be relocated to reach the Heat link. This is usually the case.

Alternatively, because it's a 12v connection between the Nest thermostat and Heat link, the wire doesn't need to be the heavy duty mains stuff. In the past, I've used the wire associated with security systems for the 12V connection, which is easier to run and conceal than twin and earth.

To keep it tidy, and give the best connection, I used 3 cores for T1 and the other 3 for T2.

 

[Jord]

Hi Stem thanks for your thoughts and expertise!

This is the hard part of the installation the end part. :-/

The current thermostat must wire up as you said to the wiring centre which is located on my top floor ( I have a townhouse style).
The thermostat is in the middle floor room
The boiler is in the utility room on the ground floor and neither areas are directly above each other - of course they aren't to make matter harder lol!

Is it possible to get 12v from the wiring centre?
For point 3 and 4 above is this at the point at where the thermostat was in the room?

thanks
Jord

 

[Jord]

The hard part i found is finding where the thermostat wires went to in the wiring station.
The thermostat wires should connect up to the heating zone valve

From what i can see there is a large wiring centre where the valves etc go to and mini version too

 

[stem]

The wiring centre is where it would normally be. As a hint, on an S-Plan system one of the thermostat wires (should be the yellow wire in your case) will normally be connected to the same terminal as the brown (Live) wire going to the central heating motorised valve.

 

[Jord]

I have attached an image of the main wiring centre where the heating and water valves go to.

in one of the images my finger is on the brown wire from the heating zone valve but this connects to a black wire.

In this wiring centre there are no wires which look like the thermostat wires particuly the wider earth variety.

I have uploaded what looks like a mini wiring centre to the other side of the water tank which has similar wires to the thermostat.

Would be great to get your further thoughts.

 

[stem]

Thanks for the photo's unfortunately I can't see which wire goes where clearly, or of course what is on the other end of them all. One problem with heating systems is that there is no fixed wire colour used for many of the connections, so it's down to the original installers personal preference. One may use a brown wire for a certain connection and another installer a blue one for the same connection.

However, one of the black cables entering from the top in picture 1 will be from the motorised valve for the central heating. Can you identify the brown wire in this cable and which terminal it is connected to?

Also, I can't see a plain yellow wire in picture 1 which would be from the room thermostat, so that yellow wire might first go to the other junction box in picture 4 and then on to the main wiring center in a different colour. Can you check this?

EDIT

Is it possible to get 12v from the wiring centre?

No there's only 230V at the wiring centre, the Heat link has an internal power supply to generate the 12v for the thermostat.

There have been at least one threads on here where a guy put a separate 12v power supply adjacent to the wiring centre and connected the 12v wiring to the thermostat to that instead of the Heat link. Not something I would personally recommend though.

 

[CBW]

Is it possible to get 12v from the wiring centre?

The heatlink sends 12vdc out, not the wiring center. So likelihood is if you want to use the existing room stat connections, then heatlink would need to go where wiring center is. As per @stem, you nee to work out which wires are connected to external controls, motorised valves etc.

 

[stem]

Well spotted @CBW you beat me to it.
The @Jord posted two consecutive posts and initially, I missed the first one of the two.

 

[Jord]

thanks for the help in the detective work

In picture 1 the black cable to the left side is from the heating valve i can confirm. and this brown wire go from there to the connector in image 3 - i am 99.9% sure.

From the section in image 4 i have broken these down...this must be where the room thermostat goes too. Then then as you mentioned diverts to the another wire which goes to the the wiring centre....definately getting warmer

Now when i find those wires from the thermostat:

I would need to connect these the wires on the other end of the connector?
is there a way i can use those existing wires to connect to the nest thermostat in the room via a 12v charge?
Would i only use the red and yellow wires and disconnect the blue?

thanks for the help - and of course i wouldn't hold you to anything discussed

 

[Jord]

thanks guys yes i could look to run 2 wires up from the downstairs heatlink to the wire centre to connect to the wires from the room thermostat....is that what you were thinking?

a challenge to say the least!

 

[CBW]

i would hold you to anything discussed

Ahh, for that reason I’m out