A:Answer The thermostat uses the voltage from your system’s wires to keep its internal battery charged, so if the power from your system is insufficient, the thermostat will run on battery for a while but will turn off features like Wi-Fi to preserve battery life before it must turn off completely. And though Nest thermostats would generally work without a common (C) wire, there are some systems that would require a C wire on the new Nest Thermostat like a heat only or cool only systems.
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