Common wire required in US?

[HestiaPi]

Was your previous thermostat battery operated? If so you may need to provide separate power to it like this:

Controlling a dumb heater (bridged wires)

An alternative to powering using USB, which can be a little challenging to get plugged/wired to the Pi because the micro USB ports are blocked I opted for a C-Wire Adapter (this is the one I bought https://www.amazon.com/gp/product/B07P3J93GQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1). It basically provides the 24v that would normally power the thermostat if you had a C wire on your unit. It works like a champ and is a little easier to wire in but most importantly, the wire is thin and ver…