DIAGNOSIS: This is almost always a power issue, specifically the lack of a common or "C" wire, or incorrect wiring with the PEK adapter.
FIX: First, you need to safely check your wiring.
- Turn off your HVAC system at the master switch or circuit breaker.
- Remove the ecobee from its backplate.
- Check if you have a wire connected to the "C" terminal. If you do, ensure it's seated firmly.
IF THAT DIDN'T WORK: If you don't have a C-wire, you must use the included Power Extender Kit (PEK). The installation for the Premium model is specific—the PEK terminal is labelled PEK+. You'll need to re-wire at the furnace control board. The ecobee app has step-by-step videos customized to your wiring setup. Use it.
HEADS UP: For any installation, always label your wires from the old thermostat one at a time before disconnecting. If you had a jumper between Rc and Rh, leave it alone—the ecobee handles that internally.