UK - replacing two wire thermostat. Nest possible?

[larkim]

My thermostat, a battery powered 7 day programmable model from Drayton, packed up yesterday.  

The wiring to this only has two cables - powered live 230v and neutral.  When switched off, the boiler lost the call for heat.  When switched on the call for heat was sent.  

Is it possible to use any of the Nest product range in the UK as a direct replacement for this without any additional wiring required?

[Frustratedddd · Accepted solution]

Simple answer no, not without altering the wiring about.

You may not have to add more cables, but you would have to configure the wiring at the programmer/boiler end.

[larkim]

Cheers, appreciate the clarity!!  Shame, but that's the way it is.  I've got a "Tado" device on order which does seem to do the 2 wire solution, so whilst I'd have preferred Nest hopefully I've got a working solution.

I guess the issue is powering the thermostat so if I need to replace batteries every 6 months or so that is the compromise!  

[Frustratedddd]

The Tado will be the same as the Nest. You asked if anymore wiring would have to be required.

The old thermostat you have can be replaced with the Nest, the wiring from thermostat to programmer/boiler would then be 12v. Simple enough. The wiring additions/alterations would be at the boiler/programmer end.  I assumed you were asking if a direct replacement was available.

[Frustratedddd]

There you go a simple wiring install.

[larkim]

The voltage at my two wires is 230v not 12v though. So presumably that rules out the nest unless I can find a way to lower the voltage.

[larkim]

 This is the old stat and it's wiring requirements.

[Frustratedddd]

Yes I understand that, but when installed correctly, the cable going from the nest display to the Nest heat link powers at 12v.

You need to investigate properly, and if in doubt find a Pro that can install.

[larkim]

Ah, there's another device? Not just a display / programmer? 

[Frustratedddd]

Yes you need to do more homework

[larkim]

You know, the whole point of me posting here was "doing my homework". And now I'm more confused than ever!! 

Where do you suggest I get the answers from that will help me with my homework if you can't give me the answer?

[larkim]

There is no programmer in my system. The existing thermostat also doubles as a timer for a 7 day schedule powered by 2 AA batteries. My understanding of the tado device is that it can be added in on that two wire loop as a direct replacement for the stat/timer that I have. 

[Frustratedddd]

The Nest is also a programmer at the display. You need to look into this closer just to make sure you get the correct one

[Frustratedddd]

The wiring diagram explains everything about installing the Nest, what is confusing?

Do you intend to install the replacement thermostat or get a professional installer?

[larkim]

My original ask was "is there a nest which directly connects to these two wires" so I could do a simple DIY job of swapping the broken unit for another. I'm not interested in anything more complex or a professional job. If nest don't make a box that does this, tado does (confirmed by their tech support) so I can DIY that device. I speculatively bought a nest box which includes a stat and receiver but will return that now.

 

 

[Frustratedddd]

Good luck with your install, by the way the picture uploaded shows a ''Hive'', don't forget you need the hub also if installing that! Exactly the same as a Nest.

[larkim]

All sorted. Brilliant setup guide on the tado device, took approx five minutes to get it all up and running including control via Google home. Wrong forum I know but really impressed so far