Nest WIRED thermostat? Any other wired smart thermostats?

grumbler

My friend asked me to replace his mechanical wired thermostat with Nest. Is this possible?

In his setting it's Drayton mechanical thermostat and Drayton programmer for CH and HW (unvented system). The thermostat has L, N and 3/CALL wires (plus Earth).

He sent me this video - https://youtu.be/dHKD-9uI24I. It says that Nest thermostat is not compatible with high voltage systems.

I also found an Installation Guide here.

Is my understanding correct, that the only way is to

• replace the existing programmer with Nest 'Heat Link' (receiver)
  
• use the existing mains voltage cable to supply 12V from Heat Link to Nest wireless thermostat?

Are there any simpler mains-powered wall-mounted smart thermostats that can directly replace a mechanical thermostat and work only like a programmable thermostat connected to the existing controller?

Neil_Jones

Nest, Hive, Honeywell or Tado are the main ones.

It may be better to consider paying somebody else to install something suitable for you.

bob_a_builder

Nest E is the one designed to directly replace an existing wired thermostat 

Just gives control of heating - not hot water like the other NESTs

This bit replaces the existing wired stat  - simple NO  / Common  connections
So its just a switch basically 
You just need to find more info on the existing stat to find out which of the 2 connections match with the switch in the existing stat




That bit communicates with the controller and actual temp sensor part as seen on this web page

https://www.toolstation.com/nest-thermostat-e/p12651

Just set the existing programmer to 24 hour Heat and then set the actual schedule in NEST app


Those videos you found refer to the US version
See these instead
Nest E UK video 
https://www.youtube.com/watch?v=1G4XDW9YG94

Nearlyold

Depends on how "Smart" you want the Stat to be  -This has load Compensation Salus RT520 Programmable Room Thermostat Boiler Plus Compliant - Hard Wired 5060103695850 | eBay

grumbler

Nearlyold said:

Depends on how "Smart" you want the Stat to be  -This has load Compensation Salus RT520 Programmable Room Thermostat Boiler Plus Compliant - Hard Wired 5060103695850 | eBay

Thank you, but by 'Smart' I mean (and my friend wants) a mobile app and remote access.

bob_a_builder said:

Nest E is the one designed to directly replace an existing wired thermostat 

Just gives control of heating - not hot water like the other NESTs

This bit replaces the existing wired stat  - simple NO  / Common  connections
So its just a switch basically 
You just need to find more info on the existing stat to find out which of the 2 connections match with the switch in the existing stat




That bit communicates with the controller and actual temp sensor part as seen on this web page

https://www.toolstation.com/nest-thermostat-e/p12651

Just set the existing programmer to 24 hour Heat and then set the actual schedule in NEST app


Those videos you found refer to the US version
See these instead
Nest E UK video 
https://www.youtube.com/watch?v=1G4XDW9YG94

Thank you - this looks good. I hate batteries, but here they seem to be for backup only.

chrisw

Thank you - this looks good. I hate batteries, but here they seem to be for backup only. 

I don't think they're for back up. They will be powering the hub bit to receive the signals from the user device and do the switching. The user device appears to be powered from a USB source so won't need batteries.

Sarahspangles

On this version of the Nest, you can additionally buy a wired stand to display/charge it - or maybe this actually recharges the batteries, but it’s the same outcome. We have the other kind of Nest and that can be wired and wall mounted. We went with wall mounting as I’m confident the cat would consider it a cat toy in any other location.

grumbler

Sarahspangles said:

On this version of the Nest, you can additionally buy a wired stand to display/charge it

This version (Nest E) comes comes with a USB-powered stand. It's the wall-mounted receiver that needs batteries.

- or maybe this actually recharges the batteries, but it’s the same outcome. We have the other kind of Nest and that can be wired and wall mounted. We went with wall mounting as I’m confident the cat would consider it a cat toy in any other location.

Yes - for 'Nest Smart Learning Thermostat' an optional stand is available. It comes with a different receiver that has to be fixed near the boiler and replaces the existing controller/programmer. In my friend's house (system boiler) it will probably require a professional installation as some changes in wiring are needed.

chrisw said:

Thank you - this looks good. I hate batteries, but here they seem to be for backup only. 

I don't think they're for back up. They will be powering the hub bit to receive the signals from the user device and do the switching. The user device appears to be powered from a USB source so won't need batteries.

Yes, you seem to be right. It's a big blow. It's a shame as the existing thermostat does have both L and N wires. Lazy Google looking for easy ways!

forgotmyname

Batteries will likely power the relay even with that the batteries should last quite a long time. Replaced a simple wired thermostat
with a digital one with a relay and the batteries have lasted approx 2 years and still going.

grumbler

forgotmyname said:

Batteries will likely power the relay even with that the batteries should last quite a long time. Replaced a simple wired thermostat
with a digital one with a relay and the batteries have lasted approx 2 years and still going.

Yes, they say 12-24 months.

Generally, the current mechanical relays consume isn't that small, but there are relays with two stable states that need power only for switching from one state to another.