Installing Nest 3rd Gen Thermostat -Worcester Bosch Greenstar 32 CDi

[howto1]

Hi All,

I'm looking to replace my existing thermostat (Worcester Bosch MT10RF-Mechanical RF thermostat) with a nest 3rd gen and wondered if you could offer some advice on the wiring of it?

1. I'd like to disable the existing receiver from the boiler which I plan to do, by removing the ribbon cable from the connection shown below, is that ok?

The connections for the nest heat link are shown below:

My current boiler connections are shown below:

Currently a L,N and E comes from an FCU underneath the boiler and connects to the white terminal block (labelled 230 V IN LNE) on the right hand side of the picture above.

2. Am I right in thinking I should take the connections that terminate into the FCU and place these into the L,N and E connections in the heat link (leaving the connections where they are in the white terminal block) and then install a new cable from the FCU and connect it to the same terminals in the heat link?

3. For the heating connections in the heat link (terminals 2 + 3). Connect terminal 2 (common) to the live in the heat link. Connect terminal 3 (heat link) to the yellow terminal block (boiler control connection), terminal CH, remove the link between the orange terminal block, terminal L and the yellow terminal block, terminal CH.

4. Now, for the hot water connections. Can I leave as they are, or do these have to be connected to the heat link as well? If so, terminals 5 + 6 (in the heat link). Connect terminal 5 (common) to the live in the heat link. Connect terminal 6 (heat link) to the yellow terminal block (boiler control connection), terminal HW, remove the link between the orange terminal block, terminal L and the yellow terminal block, terminal HW. The reason I ask is on the Worcester Bosch wiring diagram it shows a connection for the pre-heat to be made in the programmer, but I can't see any reference to this with the nest.

Worcester Bosch wiring diagrams:

Cheers

 

[Johnmdc]

Get some 5 core flex, connect brown to L, blue to N and the green/yellow to earth all on the orange connector.
Remove the two links to the yellow connector.
Connect the black to CH and grey to HW both should have a bit of brown sleeving or tape to indicate that they are live.
Leave the wires in the white connector as they are.
As you say disconnect the ribbon cable to the existing receiver.
On the heatlink connect:-
Blue to N
Brown to L and put in a link from L to 2 and from 2 to 5
Green/yellow to earth
Black to 3
Grey to 6
If you don't want to control the times of the pre-heat then don't bother with the grey wire and leave the link in from L to HW in the boiler.
But you might as well while you are at it to save the boiler coming on at all hours to keep the pre-heat warm.

 

[howto1]

Hi Johnmdc,

Thanks for the reply, will get that done this weekend then and let you know how I get on.

Thanks again.

 

[howto1]

Hi Johnmdc,

Missed your edit last night regarding the pre-heat function. I've checked the boiler manual and it appears the boiler has an eco-mode (enabled by default) which disables the pre-heat function (as well as others things I imagine). I've checked the boiler and it appears to be in eco-mode and has been since it was installed. To be honest, I've lived without the pre-heat function now for a couple of years and don't mind waiting a little while to receive hot water at the tap. So I may just not bother controlling the hot water with the nest.

Then I can just do as you said-in the boiler- remove the ribbon cable. Using a 5-core flex, connect the L,N and E from the orange connector to the L,N and E terminals in the heat link. Remove the link from the L terminal to the CH terminal (in the boiler). Connect the 'brown sleeved-black core' from the flex into the CH terminal. Tape up the grey core so it's there should I ever wish to use it in the future. Link the L from the heat link to terminal 2 and not bother putting a link in from terminal 2 to terminal 5. Connect the 'brown sleeved-black core' to terminal 3. Tape up the grey core in the heat link also. And we should be in business. The nest should control the heating and the hot water will be controlled by the boiler once a hot water tap is opened. Does that sound about right?

Cheers

 

[Johnmdc]

Spot on.

 

[howto1]

Hi Johnmdc,

Just to let you know it's all working ok.

Top man - cheers

 

[Johnmdc]

No problem, I'm glad you sorted it out.
Thanks for letting me know.

 

[Chrislj]

This looks like the same job I want to do, but with a slight twist.
I have aHoneywell theromostat linked to the Greenstar combi boiler at the moment.

Can i skip interfering with the bolier and put a spur of power from a mains socket into the L and N of the Heat Link and cut the cable from the bolier to the exsiting therostat and feed into 1 and 2 of the Heat Link and the other ends to the Nest on the wall into T1 and T2?

I suggest this as i am not sure how to open up the front of the bolier.

 

[stem]

The Heatlink should be connected to the same Fused Connector Unit and 3A fuse as the boiler. This is so that the same switch isolates them both. Otherwise there is a risk that someone may turn off the boiler FCU to work on the system thinking it is electrically isolated, but the Heatlink is still connected to the mains power. You don't have to make the connection inside the boiler it can be connected directly at the FCU. Whilst what you suggest will work, it's not good practice.

 

[Chrislj]

Thanks Stem.
FCU?
If I were to hook into the power feed to the boiler... is that the FCU?

 

[stem]

The 'Fused Connection Unit' will look something like this. It contains a switch and 3A fuse and will probably be located adjacent to the boiler.

The idea is that the same unit supplies the boiler and any associated components (eg Nest Heatlink) connected to it.

Other makes are available

Untitled

• stem
• 23 May 2012
• 1

 

[Chrislj]

That really helpful. I plan to do it this weekend. Cheers.

 

[Chrislj]

That's my FCU... power in and out and the link to the old thermostat in white and out going up from the right hand side of the fcu.

 

[Chrislj]

 

[David Fritty]

Get some 5 core flex, connect brown to L, blue to N and the green/yellow to earth all on the orange connector.
Remove the two links to the yellow connector.
Connect the black to CH and grey to HW both should have a bit of brown sleeving or tape to indicate that they are live.
Leave the wires in the white connector as they are.
As you say disconnect the ribbon cable to the existing receiver.
On the heatlink connect:-
Blue to N
Brown to L and put in a link from L to 2 and from 2 to 5
Green/yellow to earth
Black to 3
Grey to 6
If you don't want to control the times of the pre-heat then don't bother with the grey wire and leave the link in from L to HW in the boiler.
But you might as well while you are at it to save the boiler coming on at all hours to keep the pre-heat warm.

Will this work with a Worcester 40cdi early model? With a nest?
The boiler has the Worcester Bosch MT10RF-Mechanical RF thermostat fitted.

Thanks