Nest Thermostat Gen 3 Dual Zone Install

[MatthewM]

I have a Logic ESP1 35 Combi Boiler and 2 Honeywell T3 thermostats (T3H110A).
I wish to install 3rd gen nest and have purchased two.
I have read a lot on these forums of other installs.
From what I can see I need:
1. To run a L&N from the wiring centre to the HL
2. Put a jumper cable from L to 2 on the HL
3. The L&N from the stats to be removed from wiring centre and wired to T1&T2 on the HL
4. The switched live black cable on the valves removed from wiring centre and wired to 3 on the HL

The only thing I’m a little unsure of is the wiring in the nest stat. The T3 has just the two wires and appears to being powered off batteries. There is however a spare grey core of the cable behind it.

Any help would be gratefully received

Thank you

 

[ianmcd]

I have no Idea what you call HL, but what you want to do is simple, you need a Live and neutral from the heating sytem to power the nest receiver and the two existing wires in A&B from the existing thermostat go to 2&3 on the nest, do not make any links anywhere

 

[MatthewM]

HL = heat link
The thread I have been referring to is here - https://www.diynot.com/diy/threads/nest-thermostat-gen-3-dual-zone-install.601653/ is where the link was indicated as necessary. Your suggestion sounds far more straightforward. But, do the valves not need to be connected to the heat link in some way? Thank you

 

[ianmcd]

HL = heat link
The thread I have been referring to is here - https://www.diynot.com/diy/threads/nest-thermostat-gen-3-dual-zone-install.601653/ is where the link was indicated as necessary. Your suggestion sounds far more straightforward. But, do the valves not need to be connected to the heat link in some way? Thank you

They will already be connected in the wiring centre, just wire it as I already said and it will be fine, at the end of the day the nest is simply a switch, a very smart one but simply that, the two wires simply open the valve, the valve does the rest and tells the boiler when to come on, no need for a link from L&2 just use existing from A&B to 2&3 doesnt matter which way round it is as said a switch

 

[MatthewM]

Very helpful thank you. So I’m clear I take out the two stat wires on the wiring centre and wire to the 2&3 on the heat link? Wire the nest display in and job done. I was concerned my existing wiring a&b didn’t power the stat. I presume the nest will be powered from those? Many thanks

 

[CBW]

Very helpful thank you. So I’m clear I take out the two stat wires on the wiring centre and wire to the 2&3 on the heat link? Wire the nest display in and job done. I was concerned my existing wiring a&b didn’t power the stat. I presume the nest will be powered from those? Many thanks

A and b will not power the stat, unless you connect them to T1 and T2 at the heat link and alter the wiring slightly at the wiring center. Or use them on a usb lead.

 

[MatthewM]

Thank you. I still have a spare core/cable (grey one unissued behind the stat and inside the wiring centre). Please let me know what I’d need to do as I need to power them from that cable. Thank you

 

[CBW]

Thank you. I still have a spare core/cable (grey one unissued behind the stat and inside the wiring centre). Please let me know what I’d need to do as I need to power them from that cable. Thank you

Ignore the grey wire behind. Utilise the existing a and b and place in T1 and T2 on the stat and disconnect them at the wiring center making note of which is which, and place them at T1 and T2 in the heat link.

Provide the L,N and E as usual, link the L and 2, thus providing a common which needs to go to the grey and the switch live will go to the brown on the motorised valve.

I’m still learning, so hopefully my mate @ianmcd can confirm what I’ve said is correct?

 

[MatthewM]

I think that’s pretty much what I thought in my first post but it was said this was unnecessary. Thank you for your help

 

[ianmcd]

I think that’s pretty much what I thought in my first post but it was said this was unnecessary. Thank you for your help

NO as said you do not need any link, you need a cable to supply L&N for the Heat link to work and you need to connect the wires in A&B to 2&3 on the heat link, IT IS A SWITCH

 

[CBW]

NO as said you do not need any link, you need a cable to supply L&N for the Heat link to work and you need to connect the wires in A&B to 2&3 on the heat link, IT IS A SWITCH

Ian, How does this work with the zone valves and power to the Nest thermostat though?

 

[CBW]

I think that’s pretty much what I thought in my first post but it was said this was unnecessary. Thank you for your help

It needs to be setup as an S-plan, but ignoring the hot water side if things.

 

[MatthewM]

Thank you Ian. This is very helpful. As above though I presume I remove the stat A&B from the wiring centre to wire into the heat link. Will the display be powered from this though? Thank you

 

[ianmcd]

Ian, How does this work with the zone valves and power to the Nest thermostat though?

A&B is simply a switch mate (battery powered) they go to 2&3 on the heatlink, all the switch part does is send power to the Brown wire on the corrosponding Zone valve, the existing wiring will do the rest, but as said already the Heatlink needs an L&N supply to power it and if the OP wants to use T1 and T2 to power the thermostat , he /she will have to run a cable for that and supply and Earth to the Heat link

 

[MatthewM]

I presume I am to take A&B out of the wiring centre? - and wire to heat link as advised