Nest E to Heatmiser UH4

19 Nov 2021
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United Kingdom
I am new to this great forum so first of all apologies if this has already been covered somewhere else.

Here goes:
I have a WB Greenstar 8000 Life boiler for all my radiators in the house. This is controlled by a battery operated, 2-wire Nest-E which was installed by the plumber at the time the boiler went in (it's working fine although it seems that the wires at the Nest are either wrongly labelled or wrongly connected - see attached image).
I am now installing a new 2-zone wet UHF system for the house extension. This will be controlled by 2 ProTouch thermostats (240V).
Both the radiator feed and the UFH feed have been fitted with 2port zone valves.
All is fine with the connection of the new thermostats, pump and UFH valve to the Heatmiser UH4 wiring centre. However, how does the Nest E connect to the radiator zone valve and to the boiler enable with only the two wires? As it's battery run I don't want to blow it by accidentally connecting it to a live feed somewhere.
I'll attach a diagram of my system which I hope clarifies what I'm asking.
Any help will be much appreciated.

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Nest e is electrically speaking simply a battery operated on/off switch. When the receiver switches 'on' the C and NO terminals are electrically connected internally.

L (Live) = Nest e 'C' (Common)
SL (Switched Live) = Nest e 'NO' (Normally Open)

The Nest e doesn't need a connection to N or E

Can't see your photo of the existing Nest e, it's too small.
Hi Stem,

Thanks for the reply.
So I can just add the Nest to the Heatmiser Thermostat row as you describe and connect the valve to the bottom row as per the diagram?
I was worried the L of the Heatmiser top row carries a live feed from the board back to the Nest as it does for the other thermostat. or am I thinking too complicated?

Btw. the original Nest is wired brown to 'C' but with a 'NO' sticker and blue to 'NO' but with a 'C' sticker.
Looks like they've just been labelled wrongly as it works fine.

Seems straight forward....
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The 'C' and 'NO' terminals are connected to a simple on/off switch. As I said before, the two terminals are electrically connected together when the Nest e switches 'on', so it doesn't matter which way around the two wires go for it to work. Although strictly speaking, convention has it that 'C' would normally be the live (L) and 'NO' the switched live (SL)


This 'switch' inside the Heat link is rated at 230V and is isolated from the Nest e battery circuitry. See below from the Nest e spec.

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Be very carefull in what you are doing, I wouldnt recommend what you are doing as a DIY project, your boiler can be wired with OT, voltage free or 230v switching, if you get it wrong you are in for an expensive mistake, you must make sure that the boiler end is wired for 230v switching if you are going to install this setup
The Heatmiser UH4 is already connected to the boiler and is up and running, he's just adding the radiator control to a spare Zone on the UH4. Does the Heatmiser provide any control options other than 230V? I can't recall seeing anything else.

Thanks again for your valued input.

The heatmiser is only set for 230V input - no other option. It has its own fused spur from the fuse board.

Currently the boiler has only the 2 leads from the battery operated Nest going into its wiring centre so there's no other feed other than the mains power from the fuse board.

Does that make sense?
Added note:
I have not opened the boiler yet though so not sure how easy the 'boiler enable' cabling will be which I guess is what Ian is referring to?
That will of course come from the heatmiser 230v connection.
Added note:
I have not opened the boiler yet though so not sure how easy the 'boiler enable' cabling will be which I guess is what Ian is referring to?
That will of course come from the heatmiser 230v connection.
As said you will need to make sure what the existing nest E is actually connected to, if it is connected to the voltage free or OT side you will blow the boilers PCB if you connect the other end to your heatmiser, it is easy enough to refit the boiler end to the 230v side and then it will work, but make sure where the boiler side is connected to before you put mains voltage switching into it
Stem, Ian,

Again many thanks for your help. I hope I am not stretching your patience but after Ian's last comment I opened the boiler and looked at the current connections.
The existing Nest Thermostat is currently connected to 'C' and 'NO' at the Nest heatlink and the L and LR of the boiler accordingly.

With the Nest now being re-routed to the Heatmiser box (thanks Stem) I am assuming that I need to connect the Heatmiser LS to the Boiler L (grey) and the Heatmiser LR to the Boiler LR (orange)??
(of course losing the blue and brown wire currently connected to the Nest)

Ian, the boiler is labelled '230V out' at the L connection

I've attached another diagram with images of the current set-up.
When I read your original post that said "all is fine" with UFH wiring, I took that to mean that the Heatmiser was already connected and running, and you just wanted to connect the Nest-e to the UH4 for the radiators. Had that been the case the 'Heat Enable' UH4 terminals would already connected to the boiler. I see now that this isn't so and why @ianmcd raised his question.

Anyway, on a positive note, as per your photo, the Nest-e is presently connected to 230V, as L=Live Supply and LR=Live Return so corresponds nicely with the 'Heat Enable" connections on the UH4.

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