Help with installing NEST 3rd Gen with Gledhill BoilerMate II

[DirkGently1972]

I would like to replace my existing Honeywell thermostat with a nice shiny new NEST 3rd gen but am having some issues with deciphering which install diagram to follow for my Geldhill BoilerMate II heating system.

Below is a breakdown of the primary parts, components and wiring schemes...


NEST Install with Boilermate II heating system


Thermostat - Honeywell T6360B (downstairs hallway)

E = Earth
1 = Red (Live)
2 = Blue (Neutral)
3 = Yellow (Switched Live/Common?)

Honeywell Wiring Junction Box (airing cupboard)


INPUTS: (3x grey power cables - mixed core count)

1 = Red (x2)
2
3 = Blue (x2) + Black (x1) - (x1 Blue Neutral from Thermostat)
4 = Red (Thermostat Live)
5 = Yellow (Thermostat Switched Live/Common)
6
7 = Yellow
8
9 = Earth (x2)
10


OUTPUTS: (2x white heat resistant flex)

C1 = 4-core, C2 = 3-core

1 = Brown (Live) C1
2
3 = Blue (Neutral) C1
4 = Brown (Thermostat Live) C2
5 = Blue with Red collar (Thermostat Switched Live/Common) C2
6
7 = Black C1
8
9 = Earth C1+C2
10

Hot Water/Central Heating Store - Gledhill BoilerMate II

Below are some images and wiring schematics for the BoilerMate II system installed in the airing cupboard. The thermostat currently provides connections, via C1 (Neutral only) and C2 (TL, SL2 and Earth). What I need to fully understand is how I jumper these current input feeds from the HeatLink box?

NEST v3 + HeatLink System

This is how I have currently dry-wired (new cables) to the HeatLink box, following the Switched Live method described in the (online) NEST installation guide. Strangely, this is NOT shown in the paper booklet that was received with the unit and only found the copy being followed via this site.

Ignore the earth cables as I haven't got around to snipping these off yet, just in case they are required for any other connections.

After reading many posts on this (great) site I though I finally understood what went where. However, after returning tot eh airing cupboard again last night I realised/remembered that the blue cable running into the heating system, from the thermostat cable links, was not Neutral but was a Switched Live link (with red collar). This then made me wonder whether I was using the wrong diagram in the NEST guide?

I would gratefully appreciate any support or guidance on what should, in theory, be a simple drop and swap install.

Regards

 

[DirkGently1972]

And so to bed! Zzzzzzz

 

[aptsys]

Ignore the earth cables as I haven't got around to snipping these off yet, just in case they are required for any other connections.

Don't snip them off. Terminate them correctly in the earth terminal

 

[stem]

As the thermal store is kept hot permanently and there isn't any existing facility timing of the hot water, the Nest will just control the central heating. So it's simply a matter of taking the wires that presently go to your existing Honeywell T6360B and rerouting them to the Nest Receiver.

The wires you have shown "dry connected" in your photograph use the terminals your installation requires, so will be OK, provided of course that the other ends of the cables get connected to where they should go. There's no necessity for two separate neutral wires to be used to connect the same terminals, but no harm in connecting them both.

Put the two earth wires from the mains cables into the Nest earth terminal. The earth wire in the 12v cable to T1 and T2 does not need connecting to earth. [It's bad practice to use Green / yellow wires for any other purpose than earth, so it's a god job you have sufficient other wires present]

T6360B Earth = Green / yellow goes to the Nest Earth
T6360B 1 = Red (Live) goes to the Nest 'Live'
T6360B 2 = Blue (Neutral) goes to the Nest 'Neutral'
T6360B 3 = Yellow (Switched Live) goes to the Nest Terminal (3) 'Relay normally open' [Aka Call-for-heat]

Add a link wire between the Live and Terminal (2) 'Common'

Finally set the existing heating timeswitch to be 'on' permanently to prevent it interfering with the operation of the Nest.

 

[DirkGently1972]

Thanks 'aptsys' and 'stem' for your replies.

A few further questions if I may:

1. The NEST diagrams make no mention of terminating the Earth cabling to the Earth terminal, co-located with T1 and T2. Due to the potential number of cables that this little box can support, I would have assumed a beefier Earth bonding point would have been provided if required? I have absolutely no issue with doing this of course

2. I'm a little confused now about the wiring example supplied by 'stem' as I was simply going to re-use two of the existing wires that run between the Honeywell thermostat and Honeywell junction box to act as the T1 and T2 connections (specifically the RED and YELLOW wires in this case). I will then disconnect the current BROWN and BLUE (sleeved) wires that connect to the Heating system (via points 4 and 5 of the junction box) and run a new link up to the HeatLink box (now minus the earth wire shown in the earlier image), as per an example I found in one of your previous replies (stem). This then means that the Neutral (Blue) and Earth (Green/Yellow) from the old thermostat are redundant and can also be removed from points 3 and 9 of the junction box in the airing cupboard.



3. This now leaves me with the conundrum of still having three wires that somehow need to be connected back up to the heating system side, that were previously driven directly by the Thermostat wiring to drive the heating (BROWN (TL) on terminal 9, BLUE with RED sleeve (SL2) on terminal 10 and an Earth connection on terminal 12 of the heating systems wiring loom).

- So the Earth is straight forward enough, assuming I can cram all of the earth cables into that tiny little hole on the HeatLink box!

- The current LIVE input to the heating system (BROWN cable on terminal 9, above) - this is where I am stumped? Where does this wire terminate in the scheme of things

- The SWITCHED LIVE input to the heating system (BLUE with RED collar on terminal 10, above) would be fed via the HeatLink '3' output terminal?

4. Also, other than power, was the Neutral (BLUE) wire in the Honeywell thermostat used for any signalling as this was connected to a common Neutral feed into the heating system on terminal 3 of the junction box? I have assumed, as mentioned above, that this is now redundant as we are moving to a simple 2-wire 12v system stat?


I apologise for what probably seems like obvious questions. Give me a video encoder to configure or build a PoC video delivery system and I'm perfectly happy! As usual, your help and advice is always very much appreciated.

Regards

 

[stem]

1. The earth terminal is provided for the earth wires so why wouldn't you use it. There will only be two wires in it, the same as you have already managed to get in the L terminal. Don't forget what I said earlier.

The earth wire in the 12v cable to T1 and T2 does not need connecting to earth.

So either tuck it out of the way, or cut it off.

2. Don't confused by the drawing I did earlier for someone else. In fact forget it. It has no relevance to what you are doing and is not applicable to your installation. However, as you have gone to so much trouble to with your posts, I have made you a drawing for your installation. This is all you need to do. There is no need to make any changes to any other wiring other than at the existing room thermostat.



When you have done, don't forget to set the existing heating timeswitch to be 'on' permanently to prevent it interfering with the operation of the Nest.

3. I don't understand this:

This now leaves me with the conundrum of still having three wires that somehow need to be connected back up to the heating system side, that were previously driven directly by the Thermostat wiring to drive the heating (BROWN (TL) on terminal 9, BLUE with RED sleeve (SL2) on terminal 10 and an Earth connection on terminal 12 of the heating systems wiring loom).

As I said earlier, to install the Nest, there is no need to make any changes to the rest of the wiring other than at the existing room thermostat. If you have changed something else somewhere, put it back exactly as it was.

4. The neutral was provided at the Honeywell to operate a little internal heater known as an 'accelerator' in conjunction with the switched live. This was designed to improve the switching accuracy of old mechanical thermostats. It is fortunate that it is there, because the Nest receiver needs also needs it to provide the 230V to power it.

 

[DirkGently1972]

Thank you so much for taking the time to create a bespoke diagram for my specific query 'stem', it is very much appreciated

Apologies if my question caused any confusion.

For Question (4), I was attempting to describe that the NEST HeatLink will reside about 1m above the Honeywell junction box, in the airing cupboard, and that T1/T2 need to be connected to two wires from the old thermostat cable, (terminated on 4 and 5 of the junction box), as this cable does not have enough reach on it to go directly to the NEST HL box above. This means I have to disconnect the associated outputs that were terminated on 4 and 5 so that a new cable can be fed from the junction point up to the NEST HL box (to feed T1/T2). A second (NEW) cable will then be run from the NEST HL box, bypassing the junction box, directly into the heating system wiring (i.e. replacing the cable that currently sits between junction box and wiring loom of heating system - TL, SL2 and Earth). This should then tidy up the existing wiring scheme and enable me to run new wires into newly fitted trunking between the junction and NEST HL boxes.

Kindest Regards

 

[stem]

I wouldn't have initially recommended that approach for DIY because there's more scope for error.

However, it is difficult to gauge someone's competence via a forum, and as you do seem to understand what you are doing, have been able to identify the origin of the cable going to the existing room thermostat, and know which terminal each of the Red / Yellow / Blue wires come from, hopefully you will be able to manage it OK.

You can disconnect the existing thermostat cable and use it to wire up the nest thermostat to T1 & T2 so, I have modified my drawing accordingly. A word of caution though, get it wrong or mix the wires up and it will probably be difficult to resolve over a forum. Good luck!

 

[DirkGently1972]

Sir, you are a shining star!

 

[stem]

You are welcome. Just let us know how you get on in case anyone else with a boilermate they want to fit a Nest to comes along later.

 

[DirkGently1972]

I surely will.

 

[Lomer]

Hi, I have just got nest too and have the same boilermate2 with the same setup as above, just a few questions if anyone can help:

1. Is it just a case of purchasing some flex cable and wiring this into the terminal box inside the boilermate?

2. How do I reduce the voltage down going into the new thermostat?

 

[stem]

1. Is it just a case of purchasing some flex cable and wiring this into the terminal box inside the boilermate?

The wires that go to the existing room thermostat are connected to the Nest. You can use the existing cable to do this and reroute it to Nest, or you can remove the existing thermostat cable and connect your new flex to their terminals in its place. If yours is the same as the OP then the switching wires are in terminals 9 & 10.

2. How do I reduce the voltage down going into the new thermostat?

You don't. You connect the thermostat to the Heat link terminals T1 & T2 which are already 12v

Or, Nest sell a plug in power supply which is like a phone charger and you can use that instead.

 

[Lomer]

Thanks Stem, so the new stat is wired up fine now from T1, T2 so is only 12v and have tested is coming at12v.

Sorry I have noticed my setup is slightly different.

So I know I need to the blue wire SL going into the wiring centre on the wall (bottom left terminal) into the heat link.

So now all I need to do it provide the heat link with L and N, however the L going into the wiring centre in the wall (2nd from the top left) is going to a different wire in the wall - presuming this is for the boiler, same with the N (3rd down)

I just want to check that I need to at a new flex into those 2 to then go to the heat link to provide it with L&N?

Or do I need to remove from that wiring centre in the wall and put into heat link? But then there would be no L&N going to the other wire (presuming boiler).

Thanks a lot for your help!

 

[stem]

It appears that the wires in the bottom of terminals 9 & 10 are the thermostat. The cable I've arrowed should be the one that goes to the existing room thermostat. From your description, it appears to go via the additional junction box. Maybe the system has been moved or modified at sometime.

If so, then you can remove that cable completely and then the two vacant terminals connect to Nest as follows:

Terminal 9 (Marked TL for Thermostat Live) = Nest Heat link 2
Terminal 10 (Marked SL for Switched Live) = Nest Heat link 3

The power supply for the Heat link N L& E should come from terminals 1, 2 and 3

And that's it there's no need for any additional link between terminals L and 2 at the Heat link in your case that you will see on some Nest
installations.

If you have the heating clock, then the heating would need to be set to be permanently 'on' and then the Nest will take full control.