Changing Honeywell st9400c & dt92e over to nest 3rd gen heatlink & thermostat

[CliMa]

Hi,

I have a honeywell st9400c with a wireless dt92e thermostat. I'd like to change it to the Google nest learning thermostat 3rd gen. Thought it be quite simple to read the wiring diagram from the honeywell and transfer it to the heat link, but that is anything but true. I have been trying to work it out before I attempt to do it but unsuccessful. I've attached the current set up, if anyone could help me work this out I'd really appreciate it.

Regards

 

[RandomGrinch]

Your ST9400c is connected something like this:

And Nest:

First of all, power; connect:
L to L
N to N
And earth to earth.

The ST9400 has internal Live links to its relays, whereas the Nest has 'volt free' switching.
This means we need extra link wires between L and 2 and 5 on the Nest.

Grey cable in 1 to 4 on Nest
Black cable in 3 to 6 on Nest

And whatever cable joined here:

(Is it a white cable?), would go to 3 on the Nest.

You then have the option to connect the 12V, T1 and T2 connections to power the thermostat.

And the wiring to the dt92e can be completely removed.

I hope that makes sense!

 

[CliMa]

Thank you so much, for taking the time to reply! I'm going to give it a try today. I'll come back with a result.

 

[CliMa]

Worked an absolute treat! Thank you again for your help @RandomGrinch. Much appreciated!

 

[RandomGrinch]

Worked an absolute treat! Thank you again for your help @RandomGrinch. Much appreciated!

Brilliant, well done and thanks for letting us know