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

[stem]

The table looks about right to me. Personally, I would separate the thermostat 12v supplies though, so that each Heat link T1 & T2 is only connected to its associated thermostat, meaning 4 terminals are required. I imagine that each Heat link power supply is sized sufficient for powering one thermostat. It might be OK as you have shown, but I doubt they are really designed to be doubled up, and doing so might cause problems. So it would be safer to keep them separate.

So you would end up with something like:

7) T1 a
8) T2 a
9) T1 b
10) T2 b

I've used these terminal numbers as it allows a vacant terminal (for safety) to be left between both sets of 230V terminals and 12v terminals.

The rest of the wiring meets the Heat link operating criteria:

A permanent live wire connects to each Heat link L. this is its live supply
A wire joins terminal L to 2. This connects the permanent live to one side of the switch
A wire connects 3, which is the other side of the switch to the motorised valve actuator motor. When the switch turns the heating 'on' this wire becomes live and the motorised valve opens.
All neutrals connected together.

You missed 'BSR' from your nomenclature. But as it's connected to the orange wires from the motorised valves, that will be the switched live to the boiler.

 

[Pipps]

Thank you again for your confirmation and great insight.

I will also split out the T1+T2 for both Heatlinks, and leave adjacent terminals vacant between the 230v and 12v connections.

I will report back tomorrow with an update on the status!

 

[ericmark]

Reading the instruction on my Nest it seems the T1 and T2 terminals carry digital signals as well as power, it says in the readout wireless off so I would not run the 12 volt cables to any other box both thermostat and heat link pair.

Before installing my own, I would have said only use one, and use TRV heads to control zones, I have 8 zones in this house with 9 programmable TRV heads. However the Energenie Hihome head has not worked as expected, seems when Google and Nest combined the support was removed.

However it does of sorts work but not linked with the follow command. So could have used the much cheaper eQ-3 in all rooms and saved around £150.

As to zone valves I can't see the point when programmable TRV heads are used, except they also act as a relay. The problem with a non linked programmable TRV head is they can't make the boiler run, they can only stop the room heating, so the wall thermostat has to be in coolest room, where for example wind direction or sun shine can change which room is coldest there may be a case for two thermostats in parallel to ensure boiler runs when required, but gas boilers are in the main controlled by return water temperature, so with 8 zones likely one will be open most of the time so gas boiler will modulate, with just 2 however not sure it will work economically it will work but will it work taking advantage of latent head?

For me not an issue, my boiler is oil so does not modulate.

 

[stem]

Reading the instruction on my Nest it seems the T1 and T2 terminals carry digital signals as well as power

This has come up before, but I suspect that this may have only applied to the original Nest product. But no one seems to have been able to get a definitive answer even from Nest. The newer versions have the possibility of being powered by USB in which case, there won't be any physical connection between the two units and Nest's own diagram for Gen 3 version suggests that when wired, there is still radio communication, a maximum distance between them to ensure a strong signal, and a minimum distance from the boiler so that the Heat link isn't screened from the radio signals because of it.

 

[ericmark]

Removed rest for security. This is from my Nest Gen 3.

 

[Pipps]

I made partial progress today including:

• fitting a new wiring centre box to replace the tatty old one (only 10 terminals as opposed to 12, but still hopefully enough);
• rationalising then wiring into a more logical order (hopefully);
• connecting most of the cables, apart from the Nest power (to follow).

Here is the current status of the wiring (nearly completed):

Currently not yet connected but intended for first thing tomorrow morning, is to connect both Nest Hestlinks to the first three terminals as below.

And here is the full proposed wiring schematic:

I now have three questions:
1. Is it OK to connect the two BSLs ("Boiler Switched Lives") to the same terminal, or should these really be separated?
2. Should anything from the Nest Heatlink be connected to the Boiler Switched Live?
3. Does this wiring plan generally look OK?

Many thanks in advance. Hopefully this will be completed tomorrow.

 

[stem]

1. Is it OK to connect the two BSLs ("Boiler Switched Lives") to the same terminal, or should these really be separated?

There shouldn't be more than one boiler switched live (you only have one boiler don't you?) I'm guessing you are referring to the two orange wires from the two motorised valves, they both connect to the single boiler switched live, so all 3 of those wires should be connected together.

2. Should anything from the Nest Heatlink be connected to the Boiler Switched Live?

No. Otherwise I would have told you to do that. The Heat link only connects to the motorised valves, in turn the motorised valves when they have opened control the boiler. I refer you to the orange wires in 1. above.

3. Does this wiring plan generally look OK?

Yes.

 

[Pipps]

Got it Understood. Thank you

 

[Pipps]

@stem - I have one boiler. The boiler has 3-core cable running from it to the junction box. The strands are brown, black and grey.

1. Should the grey cable from the boiler be the the one that we are referring to here as the Boiler Switched Live?

2. Should this grey boiler cable be connected to the two orange cables from the valve actuators?

3. Are those two orange cables from the valve actuators definitely the valve actuator switched lives?

4. What are the two grey cables coming from each of the valve actuators? How should they be connected?

The dual zone valve actuators are Danfoss HPA2s - see manual here (PDF). The relevant wiring diagram is as follows:

I am beginning to get the feeling that everything was previously wired incorrectly.

Would the following proposed wiring plan be correct?

Thanks again for all your help.

 

[stem]

You are really are making a massive job of this. The only change that you needed to do was move 3 wires from the original thermostat and transfer them to the Heat link instead, and that's it. (apart from the connecting T1 & T2 to power the thermostat)

If it worked correctly before, the wiring would have been correct.

There is no need to change any of the wiring to the boiler or to the motorised valves, it should remain connected as it was before.

1. Should the grey cable from the boiler be the the one that we are referring to here as the Boiler Switched Live?
2. Should this grey boiler cable be connected to the two orange cables from the valve actuators?

According to your earlier photo below, the grey wire can't be the boiler switched live, it isn't connected to anything at the boiler end! The black wire is in the switched live terminal and would have originally been connected to the two motorised valve orange wires at the other end.

The boiler will require the following connections

1) A permanent live = Connects to L (Brown wire)
2) A switched live = Connects to the two orange wires from the motorised valves (Black wire)
3) A Neutral = Connects to N (Blue wire)
4) Earth

3. Are those two orange cables from the valve actuators definitely the valve actuator switched lives?

Yes

4. What are the two grey cables coming from each of the valve actuators? How should they be connected?

The grey wires should be connected to a permanent live supply. When the motorised valve opens this switch closes...

...which then makes the orange wire live, that then makes the boiler black wire live, and the boiler fires up.

 

[Pipps]

So I got my multimeter and tested every single cable for continuity. Turned out it had been wired incorrectly previously.

So I reconnected everything from scratch and neatened up all of the cables. Here is my current progress:

However, I note that you said:

The grey wires should be connected to a permanent live supply. When the motorised valve opens this switch closes...

View attachment 181223

...which then makes the orange wire live, that then makes the boiler black wire live, and the boiler fires up.

@stem - Is this now correct or should anything be changed please?
NB: The grey valve wires are not currently connected to a live.

Is this correct? Or should the grey valve wires be joined to a live?

 

[stem]

So I got my multimeter and tested every single cable for continuity. Turned out it had been wired incorrectly previously.

In which case, the system can't have been working properly before you started installing the Nests.

However, I note that you said:

The grey wires should be connected to a permanent live supply. When the motorised valve opens this switch closes...

...which then makes the orange wire live, that then makes the boiler black wire live, and the boiler fires up.

Is this now correct or should anything be changed please?

It's still correct. Both grey wires need to be connected to a permanent live. It's the only way. Without it, there won't be a live supply for the valve to send to the boiler when the motorised valve winds fully open and operates the switch.

Looks like it was correct originally with the two grey wires connected to a permanent live.

And the two orange wires appear to have been correctly connected to the black wire to the boiler switched live.

Don't forget to connect terminals (L) and (2) together at each of the the Heat links.

Where you are using green/yellow (earth) wires as live conductors [in HLCa and HLCb] you should really slide a brown sleeve over the end to indicate they are actually a live wire.

 

[Pipps]

Thank you. I have linked Heatlink (L) and (2). I will sheath both HCLas.

Should I send two permanent links from terminal 3 to terminals 4 and 5?

 

[stem]

No. These are all the connections that you need.

[terminals 4,5 & 6 are only used when the boiler is connected to a hot water cylinder.]

 

[Pipps]

I am sorry, I should have specified that I was referring to the wiring centre junction box rather than the Heatlink. Please allow me to clarify.

In the wiring centre junction box, should a link from the brown permanent live at terminal 3 to the two grey wires at terminals 4 and 5?