Despite all the “DIY” references in their marketing, Nest recommends installation by a heating technician or an electrician, in part for this reason.

Having installed a Nest myself, I recommend heeding their suggestion. I replaced a troublesome Lux thermostat with a Nest. It turns out my home’s previous owners had mislabeled the wiring, which was causing the Lux to malfunction and meant the Nest didn’t work at first. It took me about an hour to figure out the issue. A professional probably would have had it figured out in no time.