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Discuss Nest install - existing roomstat wiring in the Central Heating Forum area at PlumbersForums.net

I have a google nest (3rd gen) to replace the existing wired roomstat in my new property.

Having had a quick look at the wiring it looks like it might be a high voltage one I have? (nest says something about not being compatible with high voltage wiring?)
It has two wires plus an earth. There is a third wire that isn't connected to anything.

The boiler is a combi alpha evoke 33.

some people say it's just a case of connecting the existing wires to the nest wall plug, others say the nest heat link may be required.

i'm competent in doing the wiring if that's all that is required. however if anything is required to be done a the boiler end i'll get one of our gas engineers to do it.
 

Attachments

Brambles

Advent Win
You cannot easily instal Nest into a 240v boiler thermostat connection. To do so you use a step down transformer - which is a bit of a bodge and not always reliable.

The standard configuration to connect a third party thermostat to an Alpha Evoke boiler is 240v. Which I guess is how your thermostat is wired to the boiler.

The connection for an Alpha Control on an Alpha boiler is low voltage. This is the connection you need to use for Nest operation.

The Nest needs to wired to the boiler in the same configuration as an Alpha Controller.

This can only be done by accessing the boiler PCB/ wiring centre.

You should use a Gas Safe Registered Engineer (who is familiar with Alpha Boilers ) to make this change. It is a 15 to 20 minute job.

Hope this helps
 
ok cool, so it'll be a the nest link connected to the boiler, and then the roomstat can be placed anywhere? ie it doesn't need to physically replace the existing roomstat? (that can be just unlinked?)
 

scott_d

Plumber
Gas Engineer
The thermostat can be wired so will go in place if your old stat
Or just plugged into a socket for power.
The heat link would be positioned near to the boiler 300mm away minimum.
 
yeah but how can it be wired in place of the old stat if the wiring at the old stat is high voltage? which the nest doesn't support?
 
ah right, so the existing wiring to the old stat would be converted to low power?
so you're not talking about adding extra wiring from the boiler/heatlink to the stat location, you're mean the existing wiring would be converted from high to low voltage.

have i got that right?
 

oz-plumber

Esteemed
Plumber
You have to find out where the original thermostat wiring comes from.
If its from the boiler then you can change what voltage the wiring is connected to.
If not, then it gets tricky.

You said you were competent at wiring, but are you confident?
It could be an expensive mistake if you get it wrong.
Either to Thermostat or boiler or both
 
if it was a simple wiring up the roomstat in situ then i would do it.
as this will involve wiring at the boiler then i won't touch that.

all i know about the existing wiring is what you can see in the photos.
 

Brambles

Advent Win
See my original posting.

There are two inputs on the Alpha boiler PCB / wiring centre : 240v and low volt.

Your current thermostat is wired to 240v. That needs to be removed and a jumper inserted. You cannot change the voltage on that wiring without changing the input terminals at the boiler. The 240v feed is from the boiler.

Thereafter the Nest Heat Link is wired to the low voltage connection on the PCB. If the 240v thermostat is not fitted with a jumper ( or the existing thermostat left and turned to permanently to max), the low voltage connection will not function.

Ensure that the Heatlink is positioned in strict accordance with the installation instructions (otherwise it may not be a reliable wifi link).

I reitterate, you should use a Registered Gas Engineer to make this minor change to the PCB inputs.
 
Last edited:
yes i get that.
what i am asking is that is when the heat link is wired to the low voltage what happens to the existing wiring that runs from the boiler to the roomstat on the wall? does that wiring turn into low voltage to allow the nest stat to be situated in place of the old stat (and be powered from the existing wiring)?
 

Brambles

Advent Win
No.

The existing thermostat wiring is disconnected at the boiler and replaced with a 240v jumper.

The wiring to the existing thermostat is then redundant.

The Heatlink is wired from the low voltage terminals at the boiler and positioned as detailed in the installation instructions. The Nest is then “bound / wirelessly connected” to the Heatlink and positioned where you want it - either on a stand or wall mounted with a permanent 240v supply. You cannot use the existing 240v at your current thermostat location to power the remote Nest. That supply must be jumped on the boiler PCB to allow the low voltage thermostat connection to function ( they function in series on the PCB)

Hope this clarifies your question?
 
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ok i get it now.
so i'll be left with the existing roomstat on the wall - but disconnected and out of use.

the nest stat can be placed anywhere, but does require to be powered (via USB) - now that part is a bit of a pain.
i'd have preferred it to be wall mounted and no external wiring but hey ho, it is what it is.

so i just need to get someone to install the heat link and the rest it done by me.
 

Brambles

Advent Win
Correct.

The stand for the Nest is a decent option if you don’t want to wall mount it ( albeit an extra £20)
 
i think the main problem i was having that almost every nest install video online is american and they just connect the stat up to existing wiring and away they go.
 
i think the main problem i was having that almost every nest install video online is american and they just connect the stat up to existing wiring and away they go.
It is well worth getting an authorised NEST installer involved! It takes away all of your headaches and will give you a guarantee that the NEST will work as it should. They are doing these installs on a regular basis and know what they are doing. NEST is an excellent product and I am able to control both my hot water and heating without scrabbling about underneath the boiler!
 
update - it's all installed, and the existing high voltage wiring to the old stat was converted to low voltage so the nest could be installed in the same spot on the wall as the old stat.

i assume you don't have a combi boiler as you said you contorl your hot water too?
 
update - it's all installed, and the existing high voltage wiring to the old stat was converted to low voltage so the nest could be installed in the same spot on the wall as the old stat.

i assume you don't have a combi boiler as you said you contorl your hot water too?
Not a combi, Ideal Logic Heat 15 with hot water storage cylinder👍
 

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