Nest 3rd gen to replace existing wireless thermo on Baxi 105e

[kjacko]

Hi all,
so bagged a Nest 3rd gen in the black friday sale as our current wireless solution keeps going crazy on us, switching on/or whenever the hell it wants.

I'm not a sparky and before you all rush to tell me to get a qualified or competent sparky to wire it all in, i have a question (or two):

As i'm replacing a wireless solution already in place, and the boiler end is already wired in, should the nest heatlink just wire-in the same way as the old one, or should it all be started from scratch?
My step-son is a sparky and he may be able to steer me over the phone if its just the heatlink part that i need to wire up.
He's working away and not available for a while, but i want to get it up and running asap.

Any advice appreciated.

 

[ianmcd]

you dont say what your existing thermostat is

 

[dilalio]

so bagged a Nest 3rd gen in the black friday sale

So, @Dan Robinson you were correct

 

[Dan Robinson]

Wow an original thread where the OP has bothered to use the search button and read up on this relatively rare topic.

Oh, wait.

FFS.

 

[Dan Robinson]

So, @Dan Robinson you were correct

Dude, my hand feels like it's been run over .

 

[kjacko]

Wow an original thread where the OP has bothered to use the search button and read up on this relatively rare topic.

Oh, wait.

FFS.

Not sure if serious, but actually smarty pants I did do a search. Found one titled almost exactly like mine, but didn’t answer my query.it pertained to a new install without an existing wireless solution in place.

 

[kjacko]

you dont say what your existing thermostat is

Sorry, it’s a Towerstat RF (with a mind of its own).

 

[dilalio]

Dude, my hand feels like it's been run over .

Well it did go under the wheel!

 

[stem]

The Towerstat RF documentation I have shows it as:


The wire presently in 'Live' goes to the Nest Heat link (L) and also 'Heating common' (2)
The wire presently in 'Neutral' goes to the Nest Heat link (N)
The wire presently in 'Live output' goes to the Nest Heat link 'Heating on' (3)

Finally the Nest thermostat needs a 12v supply to power it. It can get this by being wired to the Heat link terminals T1 & T2. Don't forget the earth connection next to T1 & T2.
Alternatively you can power it by using a separate plug in power supply.

 

[kjacko]

Thanks Stem, so the existing wiring at the boiler end should/could be left as-is, i just need to follow your advice for replacing the Towerstat RF with the Nest Heat link?
The Nest thermostat will be powered by usb and linked to the heat link by wifi as it will go downstairs and the heat link will replace the Towerstat in-situ which is currently in the airing cupboard upstairs, below the baxi, which is in the loft, so only maybe a 4m run of cable between them, not really got the scope to move the heat link position.

 

[kjacko]

This is the back of the current Towerstat RF. Does your advice still apply Stem? seeing as i have wires in the bottom right connector?

 

[stem]

Yes it's still correct. Unfortunately, the original installer has also used the thermostat as a junction box, and done so badly.

All of the wires that are presently connected together will need to stay that way so electrically:

All three wires now in L connect to Heat link (L) [including one end of the red loop]
Both wires now in N connect to Heat link (N)
Both wires now in 'Com' connect to Heat Link 'Heating common' (2) [including the other end of red loop]
Black wire on its own in 'Switched live / NO' goes to the Nest Heat link 'Heating on' (3)

You will never get that many wires into the Heat link terminals. If I was doing it, I would run them to a junction box first, and then just run four single wires to the appropriate Heat link terminals.

 

[kjacko]

Understood. Sadly whilst my IT skills rock, i suck at electrics and my sparky step-son aint back from the Lakes until xmas.
I do think i can tackle this and as you suggested, with a junction box (one of the round ones?). Please could you link a picture of how you'd do it if you get chance? OR another description as above as i can follow that.
Many thanks again.

 

[stem]

Leave it with me and I'll knock up a sketch for you tomorrow, then once you have a better understanding you can decide.

I'm not a lover of the Towerstat wiring, for some bizarre reason they give the same terminals different names: 'Live Output', 'SL on', and 'NO' all refer to describe the same terminal, no wonder folks get confused.

Sadly whilst my IT skills rock, i suck at electrics.

Love that! I'm just the opposite!

 

[kjacko]

Thanks so much Stem, really appreciate it. This thing has a mind of its own and we either freeze or bake depending on its mood!