ecobee thermostats are powered from the HVAC system's 24 VAC through the C wire, and ecobee's power article covers a black screen that will not turn on, splitting a fresh installation from one that used to work. The thermostat has no battery of the kind a Nest has, so a black screen means no power reaching it. A Power Extender Kit creates a C wire from existing thermostat wiring when your system lacks a C wire and you have at least four wires at the thermostat;
The checks in more detail
ecobee's compatibility article says the PEK comes with all its thermostats except the Smart Thermostat Essential and Lite, is compatible only with 24 VAC systems and is not compatible with millivolt, high-voltage, dual transformer or fan coil or communicating systems. If the thermostat reboots repeatedly, ecobee has an article on why, usually a weak or missing C wire. Check the furnace's power switch and the breaker, the furnace door switch that cuts power when the door is open, the wires at both ends and the fuse on the control board. If you just installed it, recheck wire labels and connections.
If it worked before, check for a power cut, tripped breaker, blown fuse or a failed transformer. A PEK costs about $29.98. If you cannot find the cause, contact an HVAC pro or ecobee support. Photograph the wires on the base before changing anything so you can always return to the original layout. A thermostat that works in mild weather and fails in summer or winter points at a supply that cannot meet peak demand. If a pro installs a C wire, ask them to label it and photograph the wiring.
A photo of the wires, the old thermostat's labels and the furnace model together let a technician spot a missing C wire in minutes instead of an hour. A thermostat that has always rebooted every few minutes in a home without a C wire is telling you the wiring cannot power it, and a Power Extender Kit is the straightforward answer. Do not bypass a safety switch or the furnace door switch to get power, since those switches protect you, and if the switch is the cause the right fix is closing the door properly or having the switch checked.
Differential
Likely causes of “ecobee thermostats has power or battery problems”, and how to tell them apart
- 1
No C wire
What separates it The screen is black or the thermostat reboots because there is no C wire to power it steadily
How to confirm Install a Power Extender Kit, which makes a C wire from the wiring you already have
- 2
A tripped breaker or open furnace door
What separates it The thermostat has no power because a breaker has tripped or the furnace door is open
How to confirm Restore power at the breaker and the furnace switch, and close the furnace door properly
- 3
A blown control board fuse
What separates it The thermostat has no power because the fuse on the furnace control board has blown
How to confirm Have the fuse replaced, and have the cause of the blown fuse looked at by a qualified technician
- 4
Loose or mislabelled wires
What separates it The thermostat has never worked because wires are loose or connected to the wrong terminals
How to confirm Check the wiring at both ends against your photo and the labels, and reseat each wire firmly
- 5
A failed transformer
What separates it The thermostat stopped working because the transformer in the HVAC system has failed
How to confirm Have the transformer tested, since a failed one leaves the thermostat without any power
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the thermostat ever worked since it was installed
- The labels on each of the wires
- Whether the furnace has power and its door is closed
- Any pattern to when the thermostat reboots
Try in this order
0 of 7 completedCheck the furnace switch and breaker
ReversibleCheck the furnace switch and the breaker, and restore power if either one has been switched off.
Check the furnace door switch
ReversibleCheck the furnace door switch, because an open door can cut power to the system and thermostat.
Check wires at both ends
ReversibleCheck the wires at both ends, and match the labels on the wires to the terminals on the thermostat.
Check for a C wire
ReversibleCheck whether there is a C wire in the bundle, and if not, use a Power Extender Kit instead.
Confirm system compatibility
ReversibleConfirm the system is compatible, because the Power Extender Kit works only on 24 volt AC systems.
Check the control board fuse
ReversibleCheck the control board fuse, and if it has blown, have it replaced by someone qualified.
Contact a pro
Reversible
Model-specific
What is true of this model and not of its siblings
- PEK
- Not for millivolt, high voltage or fan coil systems.
- Power
- No battery to keep it running.
- Other models this page answers
- These steps also fit the Smart Thermostat Enhanced, ecobee3 lite.
Stop boundary
When this stops being a self-service repair
- !If it stays black after checks, contact ecobee support or an HVAC pro
- !If your system is millivolt or high voltage, PEK will not work
- !If you are unsure about the wires, hire a qualified heating and cooling technician
Evidence ledger
Sources behind this answer
Black screen and power.
PEK install.
PEK compatibility.
Reconfigure after changes.
The company and its products.
Exact questions
Common questions
Why is my ecobee black?+
A black screen means no power is reaching the thermostat, so check the breaker, the switch and the wires.
What is a PEK?+
A Power Extender Kit is a kit that makes a C wire from the wires that are already in the wall.
Which models include a PEK?+
All the ecobee models come with one, apart from the Smart Thermostat Essential and the Lite.
Which systems work with PEK?+
The kit works only with 24 volt AC systems, so check your equipment before you rely on it.
Why does it reboot?+
A weak or missing C wire is a common cause of reboots, because the thermostat cannot draw enough power.
How much is a PEK?+
It costs about $29.98 according to ecobee's page, though prices can change over time.
Can a door switch cut power?+
Yes, a furnace door switch can cut power to the whole system when the door is open or not closed.
What does Follow Me do?+
Follow Me uses the sensors to weight the rooms that have people in them, so those rooms are kept comfortable.
What is Smart Home and Away?+
It is occupancy based switching between comfort settings, using the thermostat and sensors to see if anyone is at home.
Can I add more than one sensor?+
Yes, you can add several sensors to one thermostat, and each one is assigned to a room in the app.
What is vacation mode?+
Vacation mode is a setting that holds set temperatures while you are away, and returns to your schedule when the dates end.