Do you use 2 core or 3 core for Nest Heatlink?
- Thread starter veedee
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I'm afraid it's a little more complicated than that.
The number of cores depends on which Nest you have, and whether:
you want to power the Nest thermostat from the Heat link;
the Heat link has a separate power feed from the boilers FCU;
and if your boiler has (extra) low voltage controls.
Depending on your answers, you may have a cable with between 2 and 5 cores.
Can you supply some more information about your system?
The number of cores depends on which Nest you have, and whether:
you want to power the Nest thermostat from the Heat link;
the Heat link has a separate power feed from the boilers FCU;
and if your boiler has (extra) low voltage controls.
Depending on your answers, you may have a cable with between 2 and 5 cores.
Can you supply some more information about your system?
It's the Nest v3 Learning Thermostat
To power it, I will use 2 core (no earth) and give it 12v
I used some 1mm twin and earth (as i had some lying around) and connected this to the Live and Neutral terminals in the combi boiler.
It powered the heatlink and the thermostat fine, so I presume the 0.75mm 2 core (without earth) cable will be fine also.
Why are some people using 3 and even 5 cores + earth cable?
What are the extra cores for?
I'm afraid I'm still a little confused by your description.
We have a vokera boiler with low voltage control circuitry
We want to power the Nest Heat Link from the boiler.
We want to provide the Nest thermostat with 12V power from T1 and T2 on the Nest Heatlink.
For this setup, we would need a five core cable (or a 3 core plus a 2 core) between the boiler and Heat link.
An L and N feed from the boiler to power the Heatlink.
An earth connected to the Heat link earth terminal - the MI's state the earth should be connected, if T1 and T2 are used to provide the 12V to power the thermostat.
Two more cores would be connected between Heatlink terminals 2, 3 and the boilers (extra) low voltage control circuitry.
For example:
We have a vokera boiler with low voltage control circuitry
We want to power the Nest Heat Link from the boiler.
We want to provide the Nest thermostat with 12V power from T1 and T2 on the Nest Heatlink.
For this setup, we would need a five core cable (or a 3 core plus a 2 core) between the boiler and Heat link.
An L and N feed from the boiler to power the Heatlink.
An earth connected to the Heat link earth terminal - the MI's state the earth should be connected, if T1 and T2 are used to provide the 12V to power the thermostat.
Two more cores would be connected between Heatlink terminals 2, 3 and the boilers (extra) low voltage control circuitry.
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No problem.
1. Vailliant combi boiler
2. For this setup, i used 2 core no earth cable between the boiler and Heat link.
3. L and N feed from the boiler to power the Heatlink
4. 2 Core, no earth cable then used to connect heatlink to thermostat.
Everything works great
Used 0.75mm cable. If earth is required as advised, will replace the cable at later date
I now understand why 5 cores may be used. Thanks.
Got you now!
although, there's wasn't an earth connection on the gen two Heatlink.
I believe the earth connection is an additional safety feature, that would allow an RCD to trip, if a fault occured where mains voltage found its way onto the 12V thermostat power cable - internally the earth terminal is directly connected to T1 on the Heat link PCB.
From the installation guide...
although, there's wasn't an earth connection on the gen two Heatlink.
I believe the earth connection is an additional safety feature, that would allow an RCD to trip, if a fault occured where mains voltage found its way onto the 12V thermostat power cable - internally the earth terminal is directly connected to T1 on the Heat link PCB.
Not sure I agree on that one unless I have misunderstood you. RCDs work in the absence of earthwires by seeing the imbalance of current caused by earth returns (example earth faults), a functioning stand alone 2 pole RCD in a housing does not always have an earth terminal but would still trip on a sufficient current to earth for anything on the protected side.
Note - I am saying that the RCD itself does not require an earth connection to trip. I am not saying do not earth your current using equipment for safety if it requires it.
I could definitely be wrong, but my thoughts are along the lines that the thermostat would usually be fed it's floating 12V DC, through a 2 core cable.
If mains voltage did end up on this cable, parts of the Nest thermostat may end up floating at mains potential.
If one of the cores was earthed, depending on the fault, there could be a return path to earth; causing an imbalance and allowing the RCD to trip.
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Nest Gen 3 is for both central heating (CH) and domestic hot water (DHW) the thermostat can be powered from the heat link, or another supply, when supplied from the heat link an earth is required, however 411.3.1 states "A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lamp holder having no exposed-conductive-parts and suspended from such a point." so you still need an earth to the heat link, even if not used.
Although three supplies will work, we try to have one supply for all the central heating, except when battery powered, so with a power failure my central heating is supplied from a 3.2 kWh battery and the solar panels, so will likely continue to work for months, even with no grid supply, so be it from the T1 and T2 terminals on the heat link, or a USB power supply, we want all to be powered from the same circuit. Which makes the idea of using a USB power supply rather pointless. Unless there is some way to maintain the power with a grid failure.
So in the main we are looking at least 5 core cable to supply the heat link, that is neutral, line, CH run, DHW run, and earth. Plus an extra three to the thermostat. With a Y plan, we can add a DHW off wire. With Opentherm two 0–40 volts pair, and if not 230 volt control then an extra wired for the extra low voltage supply.
Clearly, you can use Nest Gen 3 without using the DHW option, but then you could also use Nest-e, I have Nest Gen 3 and feel it is a very poor system, as when Google took over Nest they removed support for working with the Energenie TRV heads, in the USA they marketed the temperature sensor, but this has not been released for the Europe version.
I have a problem, only two cores and earth between boiler and main house, and Nest Gen 3 allows me to control DHW and CH with two wires, plus earth, however I intend to install a proper CH control in parallel with Nest, so if one room is cool, it can fire up the boiler.
Nest Gen 3 would have been ideal with last two homes, one was hot air, the other open plan, but this home it works better than what I had, but falls well short of ideal.
So step one, describe your home, does it have doors on each room? Step two describe your system, combi, Y Plan, S Plan, C Plan etc, and with that boiler type modulating or on/off, if modulating has it got the option of using opentherm?
Nest Gen 3 gives the wiring for Y and S plan, but not C, however I do have a wiring diagram for C plan.
The standard idea is to place the thermostat in a room on the ground floor (heat raises) kept cool (so it will switch off on a warm day), with no outside doors (clearly don't want it to cool when door is opened) and with no alternative heating, this incudes sun through windows. I have yet to see a home with a room which fits the requirements, so in the main we have to revert to a compromise. Like fitting in the hall, but also fitting a TRV as well.
I was lucky, I got my TRV heads while we were still in the EU, so my eQ-3 heads were £15 each, I have 5 x eQ-3, and 3 x Energenie, and 1 x Kasa (TP-Link) non link to the Nest Gen 3, the Energenie should have done, but Google removed support, did have 4, one failed, but that was due to carpet fitters.
The whole idea is to heat rooms only when required. The 9 programmable TRV heads allow that. What they can't do, is start the boiler when the room is not up to temperature. So looking at either Hive or Wiser in parallel, this is still on my to-do list.
So once you say what your aims are, then maybe we can help.
Although three supplies will work, we try to have one supply for all the central heating, except when battery powered, so with a power failure my central heating is supplied from a 3.2 kWh battery and the solar panels, so will likely continue to work for months, even with no grid supply, so be it from the T1 and T2 terminals on the heat link, or a USB power supply, we want all to be powered from the same circuit. Which makes the idea of using a USB power supply rather pointless. Unless there is some way to maintain the power with a grid failure.
So in the main we are looking at least 5 core cable to supply the heat link, that is neutral, line, CH run, DHW run, and earth. Plus an extra three to the thermostat. With a Y plan, we can add a DHW off wire. With Opentherm two 0–40 volts pair, and if not 230 volt control then an extra wired for the extra low voltage supply.
Clearly, you can use Nest Gen 3 without using the DHW option, but then you could also use Nest-e, I have Nest Gen 3 and feel it is a very poor system, as when Google took over Nest they removed support for working with the Energenie TRV heads, in the USA they marketed the temperature sensor, but this has not been released for the Europe version.
I have a problem, only two cores and earth between boiler and main house, and Nest Gen 3 allows me to control DHW and CH with two wires, plus earth, however I intend to install a proper CH control in parallel with Nest, so if one room is cool, it can fire up the boiler.
Nest Gen 3 would have been ideal with last two homes, one was hot air, the other open plan, but this home it works better than what I had, but falls well short of ideal.
So step one, describe your home, does it have doors on each room? Step two describe your system, combi, Y Plan, S Plan, C Plan etc, and with that boiler type modulating or on/off, if modulating has it got the option of using opentherm?
Nest Gen 3 gives the wiring for Y and S plan, but not C, however I do have a wiring diagram for C plan.
The standard idea is to place the thermostat in a room on the ground floor (heat raises) kept cool (so it will switch off on a warm day), with no outside doors (clearly don't want it to cool when door is opened) and with no alternative heating, this incudes sun through windows. I have yet to see a home with a room which fits the requirements, so in the main we have to revert to a compromise. Like fitting in the hall, but also fitting a TRV as well.
I was lucky, I got my TRV heads while we were still in the EU, so my eQ-3 heads were £15 each, I have 5 x eQ-3, and 3 x Energenie, and 1 x Kasa (TP-Link) non link to the Nest Gen 3, the Energenie should have done, but Google removed support, did have 4, one failed, but that was due to carpet fitters.
The whole idea is to heat rooms only when required. The 9 programmable TRV heads allow that. What they can't do, is start the boiler when the room is not up to temperature. So looking at either Hive or Wiser in parallel, this is still on my to-do list.
So once you say what your aims are, then maybe we can help.
I have disagreed with you on this before, and you have yet to convince me otherwise - unlike some other receivers (I'm talking about you, Hive), the Nest Heatlink has a cable cover and integral cord grips, although wall mountable, it is a double insulated appliance like any other.
Connected into an FCU, it would be no different to a DI, wall mounted TV.
Unless you are also trying to convince me that that should also have an unused earth connection?
The main reason the Engineers want the components powered from the same circuit, is that there is a single point of isolation for servicing the equipment.
Having ELV equipment powered by an independent USB supply, doesn't hugely increase the risk to the engineer in this case.
If there is a power failure, there is also the possibility of using power banks to supply USB devices.
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Having had a series of grid failures, having the CH still working, is a plus point. As to power banks, once one realised yes you can use them, but a grid power failure at 1 am by time one realised the house is cold, it is too late.
Apologies @ericmark I missed your response.
They have a combi boiler (Vaillant Ecotec Pro 24). Their aim was to have
1. The ability to control the central heating from their phone.
2. A thermostat that shuts off the central heating if nobody is at home
Can the Nest v3 also control the DHW on this boiler too?
I was under the impression that DHW could only be controlled if you had a setup like a System boiler/ cylinder. They would love that too
Ecotec Pro 24
Modulating
Will have to find out whether it has the option of using opentherm
Connected Nest Thermostat v3 for a mate
They have a combi boiler (Vaillant Ecotec Pro 24). Their aim was to have
1. The ability to control the central heating from their phone.
2. A thermostat that shuts off the central heating if nobody is at home
Can the Nest v3 also control the DHW on this boiler too?
I was under the impression that DHW could only be controlled if you had a setup like a System boiler/ cylinder. They would love that too
It's a flat. Each room has a door.
Combi boiler
Ecotec Pro 24
Modulating
Will have to find out whether it has the option of using opentherm
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Nest Gen 3 can control DHW, but not sure if Ecotec Pro 24 has the ability to interface with Nest, can't see why one would want to, as even when not on eco mode, the time it runs to keep water store hot is too short to worry about.
As to geofencing sorry not impressed. The ideal is to be able to set distance from home when boiler starts, but only control with Nest is the Eco and Comfort temperatures, not tested how far away one needs to be, however I turned the feature off after having a cold house as the EE mast went down in high winds.
The problem was as one walks past the thermostat it detects your home, so even if it has not detected your phone is home, it turns temp to comfort, so looking on the dial, shows heating running but not up to comfort temp. Only when I looked on PC did I realise in spite of being home, it had turned to Eco setting.
I realised that simple time settings worked better.
But the big down fall is the remote sensors have only been released for the USA version. So it only monitors one room.
So down to home design, may seem odd, but it is not heating time, but cooling time which is the problem, you can adjust heating time with the lock shield valve, you can't adjust cooling time, so the room with the wall thermostat must be the fastest room to cool.
However, it also needs to have no alternative heating, and that includes sun through windows, no outside doors, be on ground floor, and be a room always heated. In most homes no such room, but using linked TRV heads gets around the problem. However Nest can't link to any TRV heads or use remote sensors, so limited as to what homes it will work with.
As to geofencing sorry not impressed. The ideal is to be able to set distance from home when boiler starts, but only control with Nest is the Eco and Comfort temperatures, not tested how far away one needs to be, however I turned the feature off after having a cold house as the EE mast went down in high winds.
The problem was as one walks past the thermostat it detects your home, so even if it has not detected your phone is home, it turns temp to comfort, so looking on the dial, shows heating running but not up to comfort temp. Only when I looked on PC did I realise in spite of being home, it had turned to Eco setting.
I realised that simple time settings worked better.
But the big down fall is the remote sensors have only been released for the USA version. So it only monitors one room.
So down to home design, may seem odd, but it is not heating time, but cooling time which is the problem, you can adjust heating time with the lock shield valve, you can't adjust cooling time, so the room with the wall thermostat must be the fastest room to cool.
However, it also needs to have no alternative heating, and that includes sun through windows, no outside doors, be on ground floor, and be a room always heated. In most homes no such room, but using linked TRV heads gets around the problem. However Nest can't link to any TRV heads or use remote sensors, so limited as to what homes it will work with.
Or, to put it another way...
There is an adapter available, but it is not officially supported in the UK.
The boiler will still modulate, but not with the efficiency, or precision, that Vaillants own eBus controls can offer.
...and personally, I like my Nest and have had no issues with it.
No, the Nest can not control H/W on this particular combi and with DHW available on demand, there would be no benefit from doing so.
Vaillant use their own eBus system that is incompatible with OpenTherm.
There is an adapter available, but it is not officially supported in the UK.
The boiler will still modulate, but not with the efficiency, or precision, that Vaillants own eBus controls can offer.
...and personally, I like my Nest and have had no issues with it.
It's a great bit of kit.
However, in the past two years, I've experienced the following issues with my personal Nest
- Heatlink failed
- Thermostat wouldn't connect to wifi
- Thermostat wheel was stiff to turn
The above two are very common defects. Fortunately, i called google and they send me a brand new replacement unit.
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