my new ecobee enhanced won’t turn on at all after i wired it up, screen is just blank.

Diagnosis

The Ecobee Smart Thermostat Enhanced requires a constant 24VAC power supply to operate its high-resolution touchscreen and Wi-Fi radio. Unlike old mercury switches or basic digital thermostats that run on AA batteries, the Enhanced model has no internal battery backup. If the screen is completely blank, the device is experiencing a total power failure, meaning the electrical circuit between your HVAC control board and the thermostat wall plate is open.

This failure typically occurs for one of three reasons: a missing "C" (Common) wire, a tripped float switch in your AC condensate pan, or a blown 3-amp or 5-amp fuse on the furnace control board. To confirm the root cause, check your HVAC air handler; if the green LED light on the control board is off, the issue is at the breaker or fuse. If the board is powered but the screen is blank, the issue is specifically the wiring path to the thermostat.

How to Fix It

Follow these steps precisely to restore power to your device. Ensure you are working with the 24V low-voltage side of the system and not 120V/240V mains.

1. Shut off the power to your HVAC system at the circuit breaker. Verify power is off by attempting to turn on the fan manually.
2. Remove the Ecobee unit from the wall plate by pulling it straight toward you.
3. Inspect the C wire (typically blue or brown). Ensure it is firmly seated in the "C" terminal and that no copper is touching adjacent terminals, which could cause a short.
4. If no C wire is present, locate the Power Extender Kit (PEK) that came in the box. You must install this at the furnace control board. Connect the PEK wires to the R, G, Y, and C terminals on the board, then route the resulting wires to the thermostat.
5. If you have a C wire but no power, go to your furnace/air handler and locate the control board. Look for a small automotive-style blade fuse (usually 3A or 5A). If the filament is broken, replace it with a fuse of the exact same amperage.
6. Check the condensate overflow tray. If the tray is full of water, the float switch will break the R-wire connection to prevent flooding, killing power to the thermostat. Clear the drain line with a wet/dry vac.
7. Restore power at the breaker and wait 60 seconds for the Ecobee to boot.

If That Didn't Work

• Test with a Multimeter: Set your multimeter to AC voltage. Touch one probe to the R wire and one to the C wire. You should read between 24V and 28V AC. If you read 0V, the transformer in your HVAC unit has failed or the thermostat wire is severed inside the wall.
• Bypass the Float Switch: If you suspect a faulty float switch, temporarily jumper the two wires leading to the switch. If the thermostat powers on, the switch is either triggered by water or defective.
• Verify Transformer Capacity: Some older systems use a 20VA transformer which cannot handle the power draw of the Enhanced model's screen. You may need to install a 40VA 24V transformer to provide sufficient current.
• Check for "R" Wire Confusion: Ensure you are using the Rc terminal for cooling-only or Rh for heating-only. If you have a dual-system, ensure the jumper is correctly configured or that both are powered.

Heads Up

• Avoid "Battery" Hacks: Never attempt to power an Ecobee using a 9V battery or external DC adapter; this will fry the logic board instantly.
• Wire Stripping: Ensure only 1/4 inch of copper is exposed. Too much exposed wire can cause an arc-fault, blowing the furnace fuse.
• Firm Seat: Push the wires deep into the terminals until the spring clip locks them. A loose wire can cause the device to reboot randomly during high-load cycles.
• Fuse Warning: If you replace a blown fuse and it blows again immediately upon powering up, you have a direct short in your thermostat wiring. Do not replace the fuse again until you have inspected the wires for frays or staples.