My ecobee thermostat won't turn on. How can I troubleshoot?

This article applies to all ecobee thermostats except Smart, Smart SI, EMS and EMS SI.

Power issues with your ecobee may be caused by a number of things. If you're having trouble getting your thermostat to power on, choose the appropriate option below to start troubleshooting.

If you've just installed your ecobee and it is not powering on, follow the steps provided to know more about what could be causing the issue.

1. Check the power wire

With the exception of the ecobee3, the power R/Rc/Rh wire needs to be connected to the Rc terminal to power on the thermostat.


Check that all wires are properly inserted into the terminal blocks on the ecobee by giving the wires a gentle tug to ensure they’re connected. The lever on the side should be down to indicate that the wire has been properly secured.

2. Do you have a C wire?

The ecobee requires a C wire to power on. Make sure you have a wire connected to the thermostat C terminal. If you do not have a C wire, check your thermostat bundle for spare wires you can use as a C. Make sure this wire is connected to the C terminal on your HVAC control board first before using it as your C.

Can't find the C terminal on your control board? Contact support for further assistance. 


Note: If you do not see any spare wires but have the following wires: R, G, Y (you can have other wires besides these), you need to install the Power Extender Kit. Refer to our PEK Installation article to know more.

3. Did you install the Power Extender Kit (PEK)?

If you’ve installed the PEK with the ecobee3 lite, ecobee4, or SmartThermostat with voice control, verify that the wiring on your ecobee is as follows:

  • R wire >> RC terminal
  • G wire >> C terminal
  • W wire >> W1 terminal
  • Y wire >> PEK terminal


If you’ve installed the PEK, the C wire coming off the PEK must be connected to the C terminal on the HVAC control board.


4. Is the ecobee placed properly on the backplate?

Thermostat wires can sometimes prevent the ecobee from properly connecting to the backplate and cause the thermostat not to power on. Push back your thermostat wires to allow the thermostat pins to insert completely into the backplate.

You can check if the thermostat has been fully inserted if there are no spaces between the ecobee and the backplate. There should also be an audible click when the ecobee firmly connects to the backplate.

5. Check for voltage

If you’ve verified that the wiring is correct, then there’s a good chance the issue is voltage-related. You can check the voltage yourself if you have a voltmeter; test for voltage between the RC and C wires at the ecobee—anything less than 24VAC will not power the ecobee.

  • Ensure that the power is turned on from the circuit breaker
  • Some furnaces have a safety switch that cuts off power to the equipment if the equipment cover panel is not closed properly. Please ensure the cover panel of the furnace is closed properly
  • Inspect the fuse on the actual furnace control board (typically a 3 or 5 amp fuse). A blown fuse will need to be replaced
  • If you’re not using the PEK, a short in the C wire could also be an issue (often accompanied by a clicking sound at the thermostat). Try either installing the PEK or re-purposing one of your wires as a C. If the ecobee powers on, there must be an issue with the C wire itself

Note: For the ecobee SmartThermostat with voice control, there will be a green flash on the light bar to indicate that there is 24VAC power to the thermostat. If the light bar flashes green and the thermostat does not power on, contact support for further assistance.


If your ecobee was previously powered on and working fine, a sudden black screen usually indicates insufficient voltage going to the thermostat. The ecobee draws power from the furnace, so any disruption to this power source will result in a loss of power at the thermostat.

If you have a multimeter, you can test the voltage between RC and C at the ecobee—anything less than 24 VAC is insufficient. Check for the following:

1. A tripped circuit

Check your breaker box to ensure that the circuit powering the furnace isn’t tripped. If it is, turn it back on to restore power to the furnace and the ecobee should power back on.

2. A blown fuse on the furnace control board

Open the panel on your furnace to expose the control panel where your thermostat wires are connected. Most systems have a purple 3 or an orange 5 amp fuse on the board—check this fuse to ensure that it’s intact. A blown fuse will have to be replaced. Once a blown fuse is replaced, the ecobee should power back on.

3. A tripped high-limit temperature sensor

This is usually accompanied by rebooting at the thermostat during a call for heat which may also result in a complete loss of power to the thermostat. To learn more about what causes a high-limit temperature sensor visit: My furnace won’t turn on! How can I troubleshoot?

4. A tripped float switch

This is usually accompanied by rebooting during a call for cooling which may result in a loss of power completely. Inspect your float switch/condensation pump/drip pan (located at the furnace) to see if there's an excess of water or any blockage preventing the water from draining. Once this is addressed, the ecobee should power back on.



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