Google Nest Wiring (Combi Boiler UK)

[AP1990LTN]

Hi, the circuit is pretty simple however shouldn't the boiler also have a permeant feed for the hot water as terminal 3 is the switch line for central heating?

 

[UNG]

What boiler have you got fitted, most boilers have a permanent feed for pump over run after the heating is turned off to prevent heat build up in the boiler and also with a combi to run the hot water function
Boilers will usually have one or sometimes two terminals where the CH control is connected this can be either a switched live to a single terminal or a dry contact across two terminals

 

[davesparks]

Hi, the circuit is pretty simple however shouldn't the boiler also have a permeant feed for the hot water as terminal 3 is the switch line for central heating?

View attachment 103314

That diagram is purely for the basic nest wiring and does not include the rest of the wiring required for the boiler.

So yes the boiler may require other wiring such as a permanent live, frost stat, condensate pump etc depending on the specific details of your installation.