How to wire a Nest

[Russyj]

Hi,

To those who successfully managed to install this setup I was wondering how they're powering the Nest thermostats when they locate them where the existing ones were? I have 2x ESRTD3's (and a ES3247B programmer) and want to put the Nest thermostat where the old thermostat went, but as far as I can see the old thermostat runs off the mains neutral and live? Are people buying small transformers and jamming them in the wall or is there something I've missed?

Thanks!

Russ

 

[stem]

First of all if you have a programmer that also controls the hot water, the Nest Heat link replaces the programmer not the thermostat. The thermostat doesn't have all the necessary wires present. So you need to explain what your existing programmer does.

Your thermostat has 3 terminals there should be three wires connected to it:

A live wire to L
A switched live wire to N/O
A neutral wire to N

Is this what you have?

For future information. (as you are a newbie) You should have started your own thread and not Hijacked someone else's. It's against the forum rules. Don't start a new one now though, as you will then have duplicate threads going on the same subject and that's also against the rules.

 

[Milly2000]

Hi Russ,

Sounds like its possible to have the same thermostats and programmer and have them wired completely differently so I can only say what I found when I installed my Nest. As we are talking mains electricity here, unless you are certain you know what you are doing then it maybe a job that is better left to an electrician.

With my installation, I had a two circuit heating system with a thermostat for the upstairs circuit and a separate one for the downstairs circuit. Both thermostats were the same type as your setup. Downstairs in my utility room (where the boiler is located) I had an ESi programmer that was a slightly different model to you. Upstairs I have a cylinder tank in the bathroom along with the various valves to control the circuits and an ESi wiring centre.

After some experimentation I was able to determine that the upstairs wiring circuit was directly connected to my house mains electricity. The cables that supply the mains voltage to the thermostats are connected to the wiring centre (so the wiring centre distributes the power to each thermostat). Once I had disconnected the cables from the ESi wiring centre I could use them to supply the required voltage to the Nest thermostats from the Nest control box.

Yes, technically you should start a new thread, but isn't it so much better to keep all this information located in the same place? Additionally, replying to previous posts will cause those people to receive a notification which may illicit faster help!

 

[Russyj]

Hi Stem - apologies for hijacking the thread, as Milly said I thought it better to have all the information in one place in case someone (like me!) looks for this in the future, as I found this thread incredibly useful so far! You are correct in the setup, below is a picture of the physical connections:

Hi Milly - thank you for your response, that has got me thinking! I guess the question now is whether the L and N that go into the thermostat are directly spliced from the mains (in which case they are useless to me) or whether they route all the way back to the programmer where they are connected to a common connector. If it is the former I'm stuck, if it is the latter I guess I can repurpose these wires to take the output from the heatlink - I will take a look tonight! Thanks again!

For reference here is the wiring diagram as per the manual for my programmer (no guarantee this is how they've wired it!):

 

[stem]

If the above diagram is correct for your system, then you have three motorised valves connected to two central heating zones and a hot water cylinder. Not an easy system to convert to Nest, I'm afraid.

First of all, you will need two Nest Heat links, each with its own thermostat. One Heat link will control one heating zone and the hot water. The other Heat link will control the second heating zone

The existing wires going to the programmer will need to be split and redirected to the two Heat links. This will involve major rewiring and needs to be done by someone competent who fully understands the function of each wire and what it does. Unless you are really competent, this is not something that can easily be done DIY over a forum.

Looks like the mods have moved the thread anyway. Can you imagine how confusing it would be if the 100's of Nest installations on here with different solutions and installations were all on the same thread.

 

[ianmcd]

Hi,

To those who successfully managed to install this setup I was wondering how they're powering the Nest thermostats when they locate them where the existing ones were? I have 2x ESRTD3's (and a ES3247B programmer) and want to put the Nest thermostat where the old thermostat went, but as far as I can see the old thermostat runs off the mains neutral and live? Are people buying small transformers and jamming them in the wall or is there something I've missed?

View attachment 153153

Thanks!

Russ

To anyone looking at this thread, completely ignore this post it is total tosh

 

[Russyj]

Hi Ian - thanks for your useful input and for your warm welcome to these forums!

Taking an example S-plan, I'm keen to understand why my proposal won't work if I just want to control the two heating loops (leaving the hot water on the thermostat)? I want to use existing wiring wherever possible so it easy to put everything back in the future.

Standard plan:

Proposed plan (using 2 heatlinks, one coloured yellow and one green, I've fitted them into the existing plan obviously I appreciate all connections are part of one unit! Only L, N, 2, 3 channels are shown as these are the only ones of interest):

Many thanks to all!

 

[stem]

What you propose would work, but it is a poor example of a conversion.

If I understand correctly you are simply proposing to change the existing two room thermostats for two Heat links each with an associated thermostat, that will control the two motorised valves associated with the two heating zones.

In which case you are leaving an existing programmer in place that isn't really necessary and have to leave the heating part of it left permanently set to 'on' You have the facility to add the hot water timings to the Nest but you are not going to but continue to use the existing programmer to control the hot water instead.

leaving the hot water on the thermostat

The hot water thermostat stays even if you were to connect the hot water to the Heat link, Nest doesn't provide a hot water thermostat only timed on on/off control of the hot water.

I get the part about putting it all back in the future, so that would also mean leaving the original thermostats and their cables in situ to put back as well.

 

[Russyj]

Hi Stem,

Thank you very much for your input, was very helpful! It has inspired me to improve my plan, please see below. In terms of leaving it for the future, using this setup I would now leave the programmer in place but completely disconnected as it serves no purpose. As part of the current wiring loom, there are cables running to where the thermostats are (connected to pins 2, 4 and 5 currently). I intend to remove the old thermostat and put the Nest ones where the old ones sat on the wall. If I move the wire that ran from pin 2 to pin 9, an keep the wire for pin 4, and supply pins 4 and 9 with the 12V from one of the heatlinks I should be able to power these without having to install 12 converters. Only remaining question is whether the output from the heatlink has sufficient power/amps to drive 2 nests thermostats? I can't see anywhere how many amps output it has?

Thanks for your time!

 

[stem]

Glad to see you using the hot water control now.

Sorry I can't help you with the Nest Thermostat connection question. Wiring two thermostats to one Heat link is not something I've come across before. Perhaps a quick call to the Nest technical helpline may be in order here.

I did hear some 'talk' a while ago that when the Nest Thermostat was hard wired to the Heat link that it also communicated down the wires as well as wirelessly. I don't know if that is true or not, because some people spout rubbish or get the wrong end of the stick. But if it is, connecting both Thermostats to the same Heat link may cause a problem. So perhaps another reason for a quick call to the help line.

 

[Russyj]

Hi Stem,

Thanks for the feedback. I hadn't thought at all about those 12V connections being used for communication - looking online I see what you mean in mixed feedback as to whether this is the case, but there's enough doubt that I'll split these out to be sure (and call Nest to confirm as I'm curious), thank you very much for the heads up you may have saved me a new heatlink (at least!)

Russ