Another Nest installation thread

[itfcjim]

OK @CostaD this is how I set mine up in my version of layman's terms

Your HeatLink sits in the cylinder room, it has Live and Neutral feeds. When your Nest thermostat sends it a signal it sends live through to your cylinder to either the call for heat or hot water terminals

You need a Nest thermostat and HeatLink for each "zone" in your house that you want to control with Nest

Set your HeatLink up in the cylinder room:
Isolate the power
Open the circuit board box on your cylinder
Run a cable from Live on your circuit board to Live on your HeatLink
Run a cable from Neutral on your circuit board to Neutral on your HeatLink

Remove the existing cable that's going to PROGRAMMER - HW ON and terminate it with a chocblock + tape
Replace it with a cable that goes from your HeatLink "Hot Water - Call For Heat"

Remove the existing cable that's going to ROOM STAT 1 - N/O and terminate it with a chocblock + tape
Replace it with a cable that goes from your HeatLink "Heating - Call For Heat"

On the HeatLink, run a jumper cable between "Heating - Common" and "Live"
also between "Hot Water - Common" and "Live"

Repeat the instructions (minus the Hot Water bit) for any additional zones

Put all the covers back on and put your HeatLink up on the wall

Then turn the power back on, set your thermostat up and away you go


NOTE: The above instructions were what I did, after some advice above, then following the instructions and wiring diagrams that came with my Nest. I take no responsibility if you break anything Your system may be different (I really don't know much about this stuff, just know how I did mine). Once you get your head round how it works it is quite simple with a new build home where everything's wired up right. As always if you can't figure it out call a Nest Pro

Good luck

 

[Milly2000]

Hi Jim,

Sorry to resurrect this thread, but I am in the process of installing a NEST in what appears to be a similar setup (ESi controller, programmer and mains thermostats). Thanks for your extremely useful information. I intend to wire the heatlink in the cylinder room, next to the controller and leave the old programmer in its place downstairs by the boiler (for now). I would really like to use the thermostat wires to power the Nest, rather than a USB arrangement. I have had a little play with the controller wiring and it appears the 3-core wire from the thermostat points on the controller is used just for the specified thermostat. It seems to me that there is no reason not to disconnect the 3-core wire entirely, remove it from the controller and route it into the heatlink and connect up to T1 and T2. Just wondering why you didn't do this, maybe I am incorrect and this is not the way ahead?


Cheers,

Milly.

 

[stem]

I intend to wire the heatlink in the cylinder room, next to the controller and leave the old programmer in its place downstairs by the boiler

If you leave the old programmer wired in, it will be trying to control the system as well as the Nest and one will interfere with each other. It will need to be decommissioned properly. Normally the Heatlink replaces the programmer directly, as it takes over the same functions (control of one heating zone and the stored hot water) so the wires are just moved from the programmer to the Heatlink.

Your second Heatlink for the separate heating zone (ie the one that is not controlling the hot water) could go elsewhere.

You can power the associated thermostat from the Heatlink T1 and T2 if you wish, but as you have figured, if you use the existing thermostat wires for this 12v supply it will need "removing completely" from the existing system. Once the old wired thermostat has been disconnected, the heating wiring will now be 'open circuit' and the heating won't operate, so the terminals where the two switching wires to the old thermostat that have been removed from will need linking together, or the wiring modified to achieve the same thing.

Most people I have installed a Nest for seem to like the USB supply as it makes the thermostat easily movable, or they wish to have the thermostat in a different place to the original wired thermostat. Also with many installations, the existing thermostat cable may be terminated at a wiring centre that is not located near the Heatlink making its use difficult.

 

[Milly2000]

Hi Stem,

Thanks for the reply. My plan was actually to electrically disconnect the programmer (at the controller end upstairs, but initially leave the programmer on the wall to save myself some redecoration as its located in a tucked away corner of the utility room. At some stage I will remove the unit entirely, fix and paint the wall (but leave the wiring alone as it will be fully disconnected). I actually thought, originally, that I might run a single nest for downstairs and keep the original upstairs thermostat running with the original programmer, but actually a dual nest setup makes more sense.

I hadn't considered the requirement to connected the two thermostat wires together to close the circuit (so the heatlink does the job of thermostat and programmer and commands the heating via the programmer wiring block on the controller). The OP doesn't mention doing this and his setup seems to have worked? If you connect the heatlink to the ROOM STAT 1 N/O, will it not complete the circuit through the heatlink? The other two terminals seem to just be a LIVE and NEUTRAL connection.

 

[stem]

Unfortunately these systems can be wired in different ways to achieve the same thing, so whilst basic principles apply, the details of one installation may not correspond exactly to those of another.

Most programmers contain two* 'change over' switches. One for central heating and one for hot water. Like the example below.



The Nest Heatlink has the same two switches inside:



Meaning that the programmer is removed and the wires from it are connected to the Heatlink terminals that provide the same function.

*If you have two separate heating zones, plus hot water like the OP, and a three channel programmer presently, you would need two Heatlinks to provide the three switches.

I hadn't considered the requirement to connected the two thermostat wires together to close the circuit (so the heatlink does the job of thermostat and programmer and commands the heating via the programmer wiring block on the controller).

Yes exactly it has both functions in one.

If you have a wired thermostat presently, they are wired to their respective Zone Valve like this:



When the Heatlink replaces the existing programmer and the wired thermostat is removed it leaves the wiring 'open circuit' like this:



So a link is added to complete the circuit:

 

[ericmark]

Really you should start a new thread, a year ago I did not know what I know now, so possible there are errors in my first reply to this thread. As Stem says there are diffrent ways to wire central heating, Honeywell publish plans, we have Y, W, and C for example.

In the early days motorised valves were not used, and the programmer, often came with both mechanical and electrical switches to configure it as 10 or 16 programs. It was common to have no thermostat on the hot water, you just limited the time it was heated for.

So step one is to work out what you already have, in the main today we do have motorised valves, and the type and number should give one a good idea as to which system is being used.

Also the boiler, with solar power there is a good reason to retain the old idea of a header tank and cistern, but new boilers they need the return water temperature to be controlled, so there are often extra bits added. Nest is Open Therm but it would seem not that many boilers are? Some boilers are damaged by having the return water too cool, others close down if return water too hot, it is not a one thermostat fits all.

 

[Milly2000]

Yeah, I already know my setup is a little different to the OP's, its essentially the same equipment, but its been wired a little differently, and I believe in a way that will make NEST installation a little easier (as I have dedicated 3-core cable going separately to each of my two thermostats, powered from the ESI Wire centre).

I was not intending to remove the cylinder thermostat, just use the nest as a scheduler for hot water by wiring it into the programmer 'HW-ON' terminal.

 

[stem]

I was not intending to remove the cylinder thermostat, just use the nest as a scheduler for hot water by wiring it into the programmer 'HW-ON' terminal.

With a stored hot water installation, retaining the cylinder thermostat for the hot water is the same for every Nest. Nest only provides on/off control for the hot water.

 

[ericmark]

Typical wiring diagram, the S Plan followed by another typical wiring diagram the Y Plan

you will note the timer wiring is very different, trying to guess on the way it is wired does not work, and that 10 way junction box can be a nightmare. It seems electrical firms did not want to buy Honeywell wiring centres, much more common was a double back box with a length of choc block inside, trying to work out what has been done can be a nightmare. OK if the valves direct into wiring centre at least those colours are reasonably standard. As I said there are many variations, to try to fit a Nest without knowing what you are doing is asking for problems.

 

[Milly2000]

Hi,

Just to follow up, I finally got round to installing the nest thermostats. I was fortunately able to reuse the original thermostat wires so there was minimal work really required. Actually it was a straightforward job, I used the original thermostat wires for T1 and T2 to the Nests, then attached the heatlink call for heat, live and neutral to the L/1, N, N/O for the respective zones in the ESi Wiring Centre. I also bridged the Live and Common on the heatlink and finally bridged the programmer pins on the ESi Wiring Centre so everything is controlled now by the Nest thermostats. One of the heatsinks is also wired up to the hot water.

Thanks for the help, got there eventually!