Thermostat no W wire on the control unit

[Chapel976]

I’m trying to install my new thermostat as my Nest Gen 2 has been disabled by Google

I don’t have a C-wire upstairs, but I do have 2x 3-wire runs going to it (an unused white and unused green wire)

in the basement my heating system has 4 wires going to the controls but doesn’t have a W to intercept. It does have a C connection though

Could I take one of the unused wires in the 3 wire loom and connect that to C here and then wire it to the C-terminal upstairs?

[Chapel976]

it wouldn’t let me share both pics in one post.

[StopICU33]

Welcome back to the Forum! @Chapel976

I’ll tag @speadie if anyone can help answer your wiring questions, it’s speadie.

[Chapel976]

[Chapel976]

Here’s the Voltage reading off the C/R terminals on the control panel

I’m guessing this means I can take one of the spare unused wires and connect it to C down here and C up there?

[speadie]

Yes, you can use any spare wire as a C wire, as long as it is connected to C on both sides.