Nest Thermostat Gen 3 - Dual Zone Install

[R Stringer]

Hi all,

I’ve read many threads on many forums trying to piece together how my system should be wired but I’m looking for guidance from those more knowledgeable than I.

I have a new build with a Logic ESP1 35 Combi Boiler working with 2 Danfoss TPOne-M thermostats on a 2 zone valve system - upstairs and downstairs.

I have purchased 2 Nest Gen 3 Thermostats and got a quote of £160 for a nest pro to install. Though expensive I thought this was necessary due to wiring inside the boiler and removing the cover. However I’ve since realised that the wiring is done from the wiring centre under my stairs, next to the zone valves. So I’m happy to do it myself so long as I can make sure I’m wiring it correctly.

I’ve labelled where I believe the cables are from, though I would need to buy a continuity tester to make sure. The zone valves weren’t labelled but I’ve changed them to manual to confirm.

Here’s my planning so far;

is this correct so far? I think I now need to get live power to from each zone in the terminal block to the corresponding heat link at connection 3?

Above is one of the Danfoss TPOne-M thermostats. Both are wired the same. Am I correct to think I remove the red jump wire, terminate the black switched live and connect the L and N to the nest wall plate?

Any help is appreciated,

cheers

 

[stem]

Not quite. You are close, but you will also need a connection to terminal 3 of the Heat link as this is what is actually responsible for turning the heating on. If you look at the TPOne-M terminal with the black wire in it is marked NO1 (NO = Normally Open) this terminal corresponds with Nest 3 (Which is also marked Normally Open)

I'll just describe one as both will be the same. The wires currently in the TPOne-M are moved to the terminals at the Nest Heat link that have the same function as described below. You can re-route the existing cable, or disconnect the existing cable from the wiring centre and replace it with a new cable to the Nest Heat link instead, then the old thermostat cable can be used to provide the T1 & T2 connections

TPOne-M N goes to Nest N (grey wire in your photo)
TPOne-M L goes to Nest L (brown wire in your photo)
TPOne-M NO1 goes to Nest 3 Heating call for Heat (black wire in your photo)

Add a link between Nest L and Nest 2 Heating Common

Looking at your photo, The live brown wire from the motorised valve is the one that connects to NO1 (or Nest 3 Heating Call for heat) so that the valve opens when this wire becomes live. As far as I can see, the brown wires from the two motorised valves are the two I've marked in red elipses below. If so, the black wires in the same terminals should be those currently going to the two TPOne-M NO1 terminals

 

[R Stringer]

Thank you for taking the time to write such a detailed response Stem.

I’m just looking to clarify,

Are you saying that rather than adding two new lengths of cable from the blue and grey connections from the zone valves to the Heatlink L & N, I should take the grey and brown from the TPOne there, rather than T1 and T2 as I have drawn?

Below is how I was thinking with the permanent live connection between Heatlink 3 and the motorised zone valve lives. Terminating the black ones from the TP ones where indicated with a Red Cross?;

 

[stem]

Your amended photo / diagram looks good.

The blue wires to the MV are the neutrals
The grey wires to the MV are the permanent lives
The orange wires are the switched lives that control the boiler.
The brown wires from each of the MV's are the control lives that go to their associated Nest 3

The two old thermostat cables (i.e. the cables containing the black wires in that you have marked with the red X should then be completely disconnected) then, if required can be used to connect the Heat link 12v supply for the Nest thermostat T1 & T2.

 

[R Stringer]

I was planning to redirect the brown and grey wires from the old stats directly into T1 and T2, leaving the blacks unused. Is that incorrect?

 

[stem]

I was planning to redirect the brown and grey wires from the old stats directly into T1 and T2, leaving the blacks unused. Is that incorrect?

Yes, I thought that was what I said

The two old thermostat cables (i.e. the cables containing the black wires in that you have marked with the red X should then be completely disconnected) then, if required can be used to connect the Heat link 12v supply for the Nest thermostat T1 & T2.

Once the old thermostat cables are completely disconnected from the mains wiring, then you can use them to connect the T1 and T2 terminals of the Heat link to the T1 and T2 terminals of their new associated Nest thermostat. This is a 12v connection that provides the Nest thermostat with its operating power from the Heat link.

 

[R Stringer]

Just posting back to report that I followed your advice and successfully installed both thermostats working perfectly! So big thanks for your help mate. The hardest part was accessing the wiring centre which I assume has been incorrectly placed directly behind the zone valves. Squeezing the additional wiring in there and getting the cover back on was a nightmare. All working fine though. Thank you

 

[stem]

Brilliant, glad to hear it, and thanks very much for taking the time to post back to let us know how you got on. Yes, I thought the positioning of the wiring centre was interesting too.

 

[MatthewM]

Please may I very kindly ask a question. I have the same boiler and have saved this thread to install my system. But, I somehow have bought one 3rd gen nest learning thermostat and one 3rd gen pro. I’m still not sure I fully understand the difference but I wondered please which one you used for your install?
Many thanks indeed

 

[ianmcd]

Please may I very kindly ask a question. I have the same boiler and have saved this thread to install my system. But, I somehow have bought one 3rd gen nest learning thermostat and one 3rd gen pro. I’m still not sure I fully understand the difference but I wondered please which one you used for your install?
Many thanks indeed

You really should start your own post, it is against site rules to Hi-jack an old post for good reason, your boiler regardless of make will turn on when the corrosponding zone valve asks it to, your nests control the zone valves for each zone , the valves then tell the boiler when to come on

 

[MatthewM]

I have kindly asked the person who provided such helpful information about his identical install which version of the Nest they used. Nothing more.

 

[RandomGrinch]

I have kindly asked the person who provided such helpful information about his identical install which version of the Nest they used.

The version doesn't matter, the installation will be identical for both.

 

[MatthewM]

Thank you very much that’s really helpful. I will delve into it to try to find out the difference between the two versions Many thanks again