Help wiring Nest thermostat

[Nick6956]

Recently bought a Nest learning thermostat 3rd gen to replace a basic honeywell thermostat. Will be wiring to a Vaillant Ecomax 828/2 Combi boiler.

Pics and wiring diagrams attached.

Any help appreciated!

 

[stem]

The old room thermostat and its wiring is completely disconnected and removed.

Boiler terminals RT 3 & 4.....

....connect to Nest 2 & 3 (heating common and heating call for heat)

Nest also requires 230V operating power L, N & E from same L, N & E supply as boiler.

With some boilers (not all, but I don't know what category yours falls into), you would need to remove a sealed cover from the combustion chamber to access the wiring terminals. In which case the terminals should only be accessed by an RGI who can carry out the necessary safety checks to make sure the boiler is safe to use afterwards. If this is the case with yours, and you have already removed the aforesaid cover you should get an RGI to check it before use.