Google Nest 3rd Gen, Heating only - Wiring question please :)

[Gus247]

Hi all - new to the forum. Have done a bit of searching and can only find one thread 'similar' to my situation, but not exactly the same. I'll include as much information as I can so apologies if this gets wordy!

We've got a new-build house (2yrs). We have an Ideal boiler which has a Honeywell ST9100C hot water programmer and 2 x Honeywell CM707 stats (1 controls the ground floor, the other controls the middle and top floor - we're in a town house). These all connect to the Therma Q cylinder which has a valve (ESi ESZV222P) for each 'zone' and another for the hot water.

I'm happy to keep the programmer for the hot water (we tend to just leave it on constant anyway) but want to replace the two x CM707's for two x Google Nest 3rd Gen. learning thermostats. I need/would like a little confirmation/clarification please as to where the wiring needs to go.

The Brown and Black wires currently going to the stats need to be disconnected from the wiring going directly to the main board on the cylinder and re-routed to the relevant Heat Link ports T1/T2, I know this much.

I know I need to run a short link cable between L and Port 2 on the heat links.

I know I need to run a cable from port 3 on each Heat Link to the board to control the valve but not sure which connector on the board this needs to go to for each heat link.

I also need to know which cables from the board it's ok to use to provide live/neutral to the Heat Links.

I've included a load of pics and a diagram that hopefully help explain what I have


Many thanks in advance to anyone that can help!

I'm reasonably technically minded but 'as simple as possible' is always appreciated! Thank you

 

[Deleted member 267285]

You’ll need x2 Nest thermostats unless you’re planning on losing a zone? Would you be better with Nest E and just change at the thermostat?

 

[Gus247]

You’ll need x2 Nest thermostats unless you’re planning on losing a zone? Would you be better with Nest E and just change at the thermostat?

Hey CBW - apologies, I do have two Nest stats - one to replace each of the CM707's in place currently (original post amended accordingly)

 

[ianmcd]

The Live/Neutral wires currently going to the stats need to be disconnected from the wiring going directly to the main board on the cylinder and re-routed to the relevant Heat Link ports T1/T2, I know this much.

only if you want to destroy the nests, T1&T2 are 12v DC supplies to the thermostat and dont get connected to the main board as you call it, they are wired fom the nest heat link to the actual thermostat

 

[Gus247]

only if you want to destroy the nests, T1&T2 are 12v DC supplies to the thermostat and dont get connected to the main board as you call it, they are wired fom the nest heat link to the actual thermostat

T1 and T2 from the heat link provide 12v to the Nest Stats I believe?

My plan was to remove the opposite end of the wires of the stats from the cylinder-side wiring, moving that end to the T1/T2, so the stats brown/black wires go to T1/T2 - I hope that makes sense and is correct?

 

[ianmcd]

Yes that is how you do it, but stop calling then L&N wires they are not they are wires that used to be connected to L&N terminals in the wiring centre, your terminology makes it confusing what you ctually mean

 

[Gus247]

Noted and appreciated. Post edited to reflect.

Does anyone have a diagram (or link to where I may find the needed information) at all please?

Thanks in advance.