Figured it out. You need 3 wires from boiler. Live and neutral(from nest heat) get connected onto the live neutral on the boiler then the connector block next to the live neutral marked rt connect that onto terminal 3 on nest.
Then take a link of wire from the live terminal on the nest to...
Hi, would really appreciate any help on the install of the nest generation 3 to Vaillant EcoTEC pro 28. I understand that mains 230v is to be supplied to the neutral/live connections from the boiler to the nest. But where does the connections for 1/2/3 on nest get installed?