Nest wiring to a Flexicom 30cx boiler

[Robin Davies]

My son has just moved into a property where there a Glowworm Flexicom 30cx combi boiler is in place. It has been wired to a Nest heat link with the thermostat being the round, (plug-in via USB cable) unit. I am pretty savvy when it comes to wiring of these as I have recently installed a Hive system in my own house, but the way the Nest heat link has been wired intrigues (and slightly baffles) me. Wondered if anyone can comment - see attached pic. Basically the incoming mains goes via a fused switch and out of that a 2 core + earth runs to the link and, separately, another 2 core + earth goes to the boiler...seems a bit strange as I thought power should come from fused switch - through link - and onward to the boiler??

 

[ianmcd]

does it work ? looks like you are a cable short unless the cable going to the boiler is 5 core

 

[Robin Davies]

Must admit I haven't looked at the wiring behind the cover of the fused switch. Maybe it will become clear/obvious when I do. So as to be electrically safe, I guess it would be wise to disconnect incoming power to the fused switch at the consumer unit..yes?

 

[ianmcd]

is there another cable going to the boiler from somewhere else, I cant see how that set up could switch the boiler unless there is another supply powering the boiler for HW only

 

[Robin Davies]

I have just had a chance to have a good look at the way the fused switch has been wired - see attached pdf file.
Basically it is 2 core + Earth from switch to Nest and 3 core + Earth from switch to boiler. It is only set up to control Heating, not Hot water.
I would welcome any comments.. thank you

 

[Robin Davies]

I would add that I haven't physically checked the connections within the boiler but, looking at the wiring diagram for 230v thermostats in the Flexicom manual, I am assuming that is how it will be..

 

[ianmcd]

basically your boiler needs three wires, Live neutral and earth, the wires that tell it to switch on and off are controlled by the external controls no matter what they are, so you need a live neutral and earth to your boiler, and your heat link needs a live and neutral to power it , you then have another two wires that switch the boiler on and off as you use the control whatever make you choose

 

[Robin Davies]

Ian, thanks for your note. I believe I have drawn the set up correctly - from visual inspection of back plate of fused switch and Nest. It does work in practise. Have you had a look at my attached pdf file?

 

[ianmcd]

wiring looks sort of correct and should work, press the button in the middle of the nest receiver and if the boiler fires then all the wiring is correct and you have a connection control or another external control fault, all previous controls must be set to constantly on or removed and linked out

 

[Robin Davies]

Yes, when the button in the middle of the receiver/heat link is pressed, the boiler (heating) does come on. Having got this far, my son & his partner (and me for that matter!) are really struggling to get our heads round the Nest learning thermostat. I have watched a load of YouTube postings and still don't get it. We are not looking to use it as a 'learning' stat, moreover just to set up a hands-free schedule that will do the basics like come on for a period in the morning and get to a certain temp, then on again in the afternoon till late evening.
We are so frustrated that we feel that a switch to a Hive wireless stat and associated single channel receiver will be the next move!

 

[Robin Davies]

If we go to a single channel Hive receiver - and based on existing Nest wiring that is in place (as per my wiring diagram) - would I be correct in saying that a small piece of wire would be required to 'link' permanent live on the receiver to slot 1 (common) and the existing earth wire (acting a switch live) goes into slot 3 (heat on, NO)?

 

[Russyj]

Yes, when the button in the middle of the receiver/heat link is pressed, the boiler (heating) does come on. Having got this far, my son & his partner (and me for that matter!) are really struggling to get our heads round the Nest learning thermostat. I have watched a load of YouTube postings and still don't get it. We are not looking to use it as a 'learning' stat, moreover just to set up a hands-free schedule that will do the basics like come on for a period in the morning and get to a certain temp, then on again in the afternoon till late evening.
We are so frustrated that we feel that a switch to a Hive wireless stat and associated single channel receiver will be the next move!

Hi Robin,

This link may be of use to you before you give up on the Nest - you can turn the "Learning" off and just set up a schedule:
https://nest.com/uk/support/article/Nest-Sense-and-your-Nest-schedule

Russ

 

[stem]

Wiring is correct in that the wires are connected to the right places. Unless the black line shown between terminals 2 & 3 means that they are linked together...

.....in which case the heating would be permanently on.

Although the correct connections are there, some things are is a bit odd. You show a yellow wire which you call 'earth' going to terminal 3 of the Nest. Yellow is not the colour of an earth wire and it is actually a switched live. So not sure why you would call it an earth.

Then you show other yellow wires that are actually being used as an earth that should be green / yellow stripe.

Earth Wire

Live Wire

 

[Robin Davies]

Hi Stem, thanks for your note. No, the small black line is not a physical link in the Heat link - it is just me 'completing the circuit' on the diagram for my own understanding for when heat is on! In the cable that runs to the Heat Link, the installer has used the earth wire to act as the 'switch live' as it is joined to black (in the fused switch box) which, in turn, goes to 'R' (switch live) on the boiler.
The set-up on the Flexicom is a bit different to what I have done recently (when installing a single channel Hive receiver to my own Worcester 30CDi) in that (aside from permanent live, neutral & earth) there is essentially only one wire involved, connected to 'R' (switch live) at the boiler end. As the name implies, it makes (brings on) or breaks the live supply to and from receiver and boiler. Correct?