Clock is set to on (sun) which is what it was on before. Will try that, but sort of expect it to just turn central heating off, the wiring diagram shows them serially, so if either is off, the boiler should not fire.
From what I'm seeing somehow, it feels like Boiler 4 (call for heat) is...
Thanks Jackthom,
I replicated what how my old drayton scr was setup as they had identical labels this gave:-
Boiler L to Heatlink L
Boiler N to Heatlink N
Boiler 3 to Heatlink 2
Boiler 4 to Heatlink 3
As far as I can see this just means I'm pulling in power in a slightly different way...
Apologies for resurrecting this thread but am looking for the definitive answer to the Nest / Vaillant connections!
Can someone confirm that the 'MikeyD method' is:-
Boiler 3 to Heatlink L
Heatlink L to Heatlink 2
Boiler 4 to Heatlink 3
Boiler 5 to Heatlink N
See image below
From MikeyD's...