Nest Installation - Understanding my wiring

24 Nov 2018
Reaction score
United Kingdom
Hi All,

Recently moved into a new house and hot water is not triggering the boiler to fire up. Not sure what's causing this but since I wanted to install Nest anyways I thought I'd get this done and see if the problem remains.
My System has a hot water tank with 2 motorised valves and as per my understanding this is an S-Plan system. Problem I have is that when I took off the RWB9 controller I didn't see a wire connected to the hot water connector 1. I was expecting one like there is on connector 4 which will operate the valve for the CH. Any help is most welcome :)
I'm attaching photos of my system.


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4 is CH on, 3 is HW on, 2 and 1 are not used.

Assuming it was wired correctly and did work in the past, no HW is one of:
cylinder thermostat set incorrectly, broken, or the water is already hot
motorised valve for the HW has failed, or the switch inside has failed
programmer has failed and isn't switching L to pin 3.
  • Thanks
Reactions: CBW
you have it wrong 1 on your existing programmer is HW off not used on an S plan, 3 is HW on
  • Thanks
Reactions: CBW

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