How to connect two new Nest 3rd gen heatlinks? (photos)

should a link from the brown permanent live at terminal 3 to the two grey wires at terminals 4 and 5?

Eh?? you said you were using wiring terminals 4 and 5 for the 2 x Heat links 'heating call for heat'


Don't see any grey wires at terminals 4 & 5, they appear to be the brown wires to the motorised valves which looks correct as they should be connected to the 'heating call for heat' at their respective Heat link.


Anyway, it doesn't matter what number terminals you personally choose to use. However, The grey wires from both motorised valves need to be connected to a permanent live. Please don't ask this question again, I've told you several times already.

I like to think the best of people but I'm starting to think you are winding me up.
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Please be assured that I am not winding you up. I just do not want to make a mistake.

I will run two links from the permanent live to terminals 4 and 5 on the junction box.
OK, in that case, here's a wiring diagram for your complete system. The connections at the wiring centre can be in any order, provided the wires are connected to each other as shown. I've omitted the terminal connections for both sets of T1 and T2 for clarity as they just go straight through.

2 HL's Model (1).jpg
Wow, thank you so much! I can't wait to work through this to double check that everything is correct before I fire it up. I am sure that this will be useful for many more people too :)
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@stem - Everything appears to be wired correctly.

The Nests work and make the boiler to fire up just fine.

But the boiler will not switch-off when the Nests tell it to.

What could be the most likely cause?
Here are a few basic things that might help. First of all was the system working OK before the Nests were installed, or was this problem already present?

Have you checked the wires carefully to make sure that they all go to where they should? Heat link terminals 1,4,5 & 6 should not have any wires in them.

Are the motorised valves in the 'Auto' position and not manually locked open.

Have you changed the wiring at the boiler terminals at all, or is it exactly as it was before you started?

When you say that the Heat links don't turn the boiler off. When they should be off and the boiler is still running. What lights are showing on the Heat link?


Circle = Power on
Waves = Heating on
Drip = Hot water on. (not connected in your case but the light may still come on)

What happens when you switch both Heat links 'on' and 'off' manually using their large central buttons? Try with them one at a time. Start with both of them off. Turn on Heat Link a with the button. Does the boiler come on? now turn it off. Does the boiler go off? repeat the test with Heat link b. If they work as they should, then wiring is correct.
@stem - Thanks for the detailed advice. I will investigate first thing tomorrow morning and report back.
What happens when you switch both Heat links 'on' and 'off' manually using their large central buttons?
Thanks, did not realise the centre button would switch it on, did not even realise it was a button, had the heating engineer here yesterday and he clearly did not know either, I phoned my wife to turn heating on.

I do note with Nest two things which may be relevant here, one there is a delay using the computer to it actually switching one, and two it will not switch on until the internal batteries have charged, did not take long maybe 15 minutes, but turned off power to ensure cold when plumbers came to fit the motorised valves, and on completing it would not turn no straight away.
Anything to report yet??
Thanks for thinking of this. I have nothing whatsoever to report yet.

This house refurbishment project took an unexpected turn several weeks ago.

I have spent the last few weeks rewiring the lighting and replastering.

Believe me when I say that I cannot wait to return to the Nest!

You will be the first to know once I have switched it on again.

Thanks again and please keep watching this space...
@stem - Update at last after finally being able to visit the property again.

Combi boiler is connected to two zone valves and two Nest units - Zone 1 is living room a Zone 2 is rest of flat.

When turning on the central heating at the consumer unit and turning both Nest controls to max, all radiators in both zones get hot.

But when turning off Zone 2, only Zone 1 cools down. Zone 2 continues to be fully hot.

Upon swapping both pairs of TP1 and TP2 wires between both Nest base units above the wiring centre, the result remains exactly the same.

That is, when the Zone 2 Nest control is disabled and the Zone 1 remains set to full, Zone 2 switches off and Zone 2 remains fully hot.

That is exactly the same outcome either way, regardless of which way around the Nest base units are connected to the wiring centre.

Are the Nest thermostat control dials fitted onto the Nest wall mounts in the wrong order? But surely they communicate with the Nest base units only via the cables.

Could it be that the zone valves are connected to the wiring centre incorrectly? Should they be connected separately somehow?

What is the problem and what should be done to rectify this please?



The final section of this Nest support page for the Nest Learning Thermostat says the following:

"If your Nest thermostat is installed on the wall and connected to your old thermostat’s wires, it will use both the wires and wireless Thread to communicate with the Heat Link."

I will switch over the thermostat faceplates and see if it then operates correctly. More to follow.
I think @ericmark is right. T1 & T2 primarily provide the thermostat with power and the are not essential connections, because a separate 12v power supply could be used, in which case, the thermostat will still communicate with the Heat link. And, as you say from the support page, and also as the diagram below shows, some communication is still wireless.


But it's easy to rectify, either swap the thermostats over, or the motorised valve heads. [but not both!]
@stem - Thank you for the authoritative confirmation.

I will switch the thermostats tomorrow and report back.

One final question: Should I upgrade the boiler to OpenTherm?

Apparently it takes just a wiring harness. But is it worth it?

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