Why Your Smart Thermostat Won't Stay On

Cool Talk with Hartzell's | Your HVAC Questions, Answered! · Jul 20, 2026 · 17m · transcript

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I get calls all the time from folks whose new smart thermostat will not stay on, keeps rebooting, or goes dark for no reason. Almost every time the thermostat is fine. What is missing is the C-wire, the common wire that gives a smart thermostat the steady power it needs to run its screen and WiFi around the clock. In this episode I explain what the C-wire actually does, why old dial thermostats never needed one, how to check whether you already have one hiding in your wall, and your options if you do not. If your smart thermostat is acting haunted, listen before you box it up…