Burnham Alpine Boiler and C Wire for Nest

johnfromwtown

I once connected a Nest smart thermostat to a gas fired boiler by running a new 5 (?) strand wire from the T-stat to the boiler and attaching all the colored wires in the corresponding colored slots. Easy!

Now in a different house I want to do the same thing, but my problem isn't with snaking the wire through the wall, but not knowing where to connect within my Alpine ALP080B boiler. As the diagram and picture shows (hopefully), I have a Red and White wire connecting my Honeywell thermostat to my heat-only system. A green wire in that three-strand bundle is not used; it's unattached. The three-strand T-stat wire runs to an electrical junction box in the cellar where the T-stat Red and Green wires are linked by a wire connector with the Red line from the boiler. Another connector links the White wires from the T-stat and Boiler. The wire from the boiler has only a Red and White wire.

The photo shows those Red and White wires attached to the slots labeled "Heating T-Stat" in the boiler.

So what do I do? I would run a new 3-strand wire from the Nest thermostat, bypass the junction box, and go directly to the boiler, but I don't know where to put that common wire. Nest has a power connector but even that seems like it needs a place to attach to that the Alpine seems to lack. Any help would be appreciated and apologies if this has been covered already. (I did search first.) Thanks in advance.