Hello Makrothumia,
Thanks for reaching out here in the Google Nest Community Forum. Help's here!
In most heating, ventilation, and air conditioning (HVAC) systems, the X2 wire typically refers to the second stage of heating. It's commonly used in systems with two stages of heating to provide better temperature control and efficiency. To get a better look, please share with us a photo of your thermostat's wiring and tell us the make and model of your HVAC system.
I'll look forward to your response.
Regards,
Mark
