Dead Nest? The Nest thermostat has an internal battery which can usually be charged by the 24v heating and cooling wires coming from your homes HVAC system. Problems arise when there are too many components borrowing from the same power source. The Nest learning thermostat is a power stealing thermostat which can cause system malfunction or improper system operation. The solution is to add what is known as a common wire, this wire is a separate 24 volt supply dedicated to charging your Nest thermostat. Although Nest claims this wire is not necessary with all installations A.J. LeBlanc Heating would highly recommend it to anyone using any smart thermostat. Installing a common wire can range in difficulty - if the thermostat wires are inaccessible from the power source walls may need to be opened or an alternative thermostat location may be suggested.