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Thermostats · Ecobee Thermostats

Ecobee Thermostat Not Turning On? 6 Causes and How to Fix Them

Ecobee thermostat not turning on? Close the HVAC cover panel, tug-test each wire, move a lone R wire to Rc, and check the C wire or Power Extender Kit.

By Evrenus Fırat PolatEditor & ResearcherPublished Checked against 1 manual + 9 manufacturer pages + 1 government source

Quick answer

An ecobee runs on power from your heating and cooling system, so a dark screen means that power is not reaching it. Check the breaker and switch, close the equipment cover panel and tug each wire. A single R wire must sit in Rc. Without a C wire, the thermostat needs a correctly wired Power Extender Kit.

Check these first:

  1. Is the HVAC cover panel closed?
  2. Wires tug-tested in their terminals
  3. A single R wire goes in Rc
Time to fix
5–60 min
Difficulty
Easy, 1 of 4
Safety
WarningElectrical
On this page · 12 sections

An ecobee needs a steady 24-volt supply from the heating and cooling system, and ecobee says not all homes have the C wire that supplies it.⁠[1] So when an ecobee screen stays dark, the question is where the power stops: at the breaker, at the equipment's cover panel, at a loose wire or at the C wire. ecobee's own install pages list the checks for a thermostat that does not turn on, and this guide works through them.⁠[2] For ecobee model differences, see ecobee thermostat basics.

Before you start

Know which ecobee you have. The Power Extender Kit (PEK) comes in the box with every ecobee except the Smart Thermostat Essential and Smart Thermostat Lite, which can still use one bought separately.⁠[1]

Shut-offs

  • Power

    The breaker for the furnace or air handler, or the switch near the equipment that looks like a light switch.

You'll need

  • LED work flashlight
  • Furnace air filter

Which ecobee needs what

The PEK's role differs by model. ecobee lists these models as compatible with the kit.⁠[1]

ecobee modelPEK in the box?Without a C wire
Smart Thermostat PremiumYes⁠[1]Install the included PEK
Smart Thermostat EnhancedYes⁠[1]Install the included PEK
Smart Thermostat EssentialNo, sold separately⁠[4]PEK required for homes without a C wire
Smart Thermostat LiteNo, sold separately⁠[1]Compatible with a PEK bought separately
ecobee4, ecobee3 lite, ecobee3Listed as PEK-compatible⁠[1]Check the C wire or PEK wiring
Fig. 1How thermostat wires connect to the furnace and AC
How thermostat wires connect to the furnace and ACWiring schematic of a wall thermostat connected to a gas furnace control board and an outdoor AC unit. Twelve numbered parts, following the power: 1 service switch on the 120-volt supply below the furnace; 2 door switch on the blower door; 3 transformer on the control board, making 24 volts; 4 fuse on the board; then the thermostat terminals, top to bottom: 5 R wire bringing 24-volt power; 6 Rc jumper joining R and Rc; 7 C wire, the common return; 8 W wire for heat; 9 Y wire for cooling; 10 G wire for the fan; 11 O/B wire, used only by heat pumps and empty here; 12 outdoor unit, fed by the Y and C wires from the furnace terminal strip. Dashed lines are 24-volt thermostat wires; thick solid lines are 120-volt power.ThermostatRRcCWYGO/BFurnaceRCWYGYC123456789101112Service switchDoor switchTransformerFuseR wireRc jumperC wireW wireY wireG wireO/B wireOutdoor unit

  1. Service switch and breaker DIY

    The furnace runs on household power from a breaker, usually through a switch that looks like a light switch near the unit. If either is off, the thermostat loses its 24-volt supply too.[8][9]

  2. Blower door switch DIY

    A switch pressed by the blower access panel. With the panel off or loose, it cuts power to the control board, so nothing runs and a wired thermostat may go blank. Never tape it closed.[9][8]

  3. Transformer Pro only

    Turns the furnace’s 120-volt supply into the low voltage the thermostat circuit uses. Honeywell says thermostats work on 20 to 30 volts AC; a reading outside that range is a job for a professional.[9][8]

  4. Control board fuse Pro only

    Many boards protect the 24-volt circuit with a small fuse (3 amps on the Bosch furnace). A short between thermostat wires during an install can blow it, and then the thermostat and the system both go dead.[9]

  5. R (power) DIY with care

    Brings 24-volt power from the transformer up to the thermostat. Every call for heat, cooling or fan starts by connecting R to another wire.[8][10]

  6. Rc and the R/Rc jumper DIY with care

    With one R wire, R and Rc must be joined by a metal jumper or a selector set to 1 Wire. With separate R and Rc wires, the jumper comes out or the selector goes to 2 Wire.[8][10]

  7. C (common) DIY with care

    The return path to the transformer. Smart thermostats need it for steady power; if your old thermostat had no C wire, it is probably not connected at the furnace either. Running a new one generally needs a pro.[8][11]

  8. W (heat) DIY with care

    When the thermostat connects R to W, the furnace starts its heating sequence. On a heat pump, heat is called through Y and O/B instead.[10][9]

  9. Y (cooling) DIY with care

    Calls for cooling. At the furnace, Y connects on to the outdoor unit, where it starts the compressor.[9]

  10. G (fan) DIY with care

    Runs the furnace blower by itself, as when the fan switch is set to On. In heating and cooling, the board also starts the blower on its own timing.[9]

  11. O/B (heat pumps only) DIY with care

    Heat pumps use O/B together with Y to switch between heating and cooling. On a furnace with a plain AC like this one, the terminal stays empty.[10][11]

  12. Outdoor AC unit Pro only

    Its low-voltage pair (Y and C) lands on the furnace terminal strip, not on the thermostat. A cooling call on Y energizes the compressor.[9]

  • Before you touch a wire. Turn the system off at its breaker or switch first, and note which terminal each wire came from. Wire colors are a habit, not a rule; go by the terminal letter.[11][8]
Every thermostat wire also lands on the furnace terminal strip. A single R wire goes in Rc on an ecobee.

  1. Power to the heating and cooling system is off

    Most commonDIYTime: 5 min

    The breaker or the light-switch-style switch near the equipment is off.
    Fix it: Power to the heating and cooling system is off

  2. HVAC cover panel not fully closed

    CommonDIYTime: 5 min

    The equipment will not turn on with its panel loose.
    Fix it: HVAC cover panel not fully closed

  3. Loose wire in a terminal block

    CommonDIY with careTime: 15 min

    A wire that slipped out or never seated in its terminal.
    Fix it: Loose wire in a terminal block

  4. A single R wire in the wrong terminal

    CommonDIY with careTime: 5 min

    One R, Rc or Rh wire that is not in Rc.
    Fix it: A single R wire in the wrong terminal

  5. No C wire, or the Power Extender Kit is miswired

    Less commonDIY with careTime: 30–60 min

    A home without a C wire, or a PEK with loose or swapped connections.
    Fix it: No C wire, or the Power Extender Kit is miswired

  6. A system the PEK cannot power

    Less commonPro only

    Millivolt, high-voltage, dual transformer, fan coil or communicating equipment.
    What a pro does: A system the PEK cannot power

Turn the system power back on

ecobee's install steps begin and end at the system's power switch: off before wiring, then turn your power back on at your heating and cooling system when you are done.⁠[2] A thermostat installed, or worked on, without that last step stays dark.

  1. Find the switch or breaker for the equipment

    • Time: 3 min
    • LED work flashlight

    ecobee says it is usually a light switch or a breaker panel.⁠[3]

    You'll know it worked when: You know which breaker or switch feeds the furnace or air handler.

  2. Turn it fully on

    • Time: 1 min

    Reset a tripped breaker once. If it trips again, leave it off and call a pro.

    You'll know it worked when: The breaker or switch is firmly in the On position.

  3. Watch the thermostat for a minute

    • Time: 2 min

    If it stays dark, go to the cover panel next.⁠[2]

    You'll know it worked when: The ecobee screen lights and starts up.

If you can't find a switch, look on the side of the furnace or air handler and on nearby walls. Label it once you find it, so the next person does not hunt for it.

Still not fixed? Next likely cause: HVAC cover panel not fully closed

Close the HVAC cover panel

This one catches many people right after an install or a filter change. ecobee says some systems will not turn on if the cover panel has not been closed properly.⁠[5]

  1. Go to the furnace or air handler

    • Time: 2 min

    The panel is the removable door on the front of the unit.⁠[5]

    You'll know it worked when: You can see the front cover panel.

  2. Seat the panel flat and latch it

    • Time: 2 min

    ecobee says to make sure your HVAC cover panel is closed.⁠[6]

    You'll know it worked when: The panel sits flush on all sides and is fully closed.

  3. Check the filter while you are there

    • Time: 5 min
    • Furnace air filter

    ENERGY STAR says to change a dirty filter, or at least every 3 months.⁠[7] Close the panel again afterward.

    You'll know it worked when: The filter is clean, or a new one is in.

If the panel was off for a filter change or a repair, the whole system, the ecobee included, can stay off until the panel goes back on properly.

Still not fixed? Next likely cause: Loose wire in a terminal block

Tug-test every wire

ecobee thermostats use push-in terminal blocks. ecobee's first troubleshooting step is to check that all wires are properly inserted into the terminal blocks, and to tug on them to ensure they are not loose.⁠[2]

  1. Turn off the system power

    • Time: 2 min

    Do this before you take the thermostat off its backplate.⁠[3]

    You'll know it worked when: The breaker or switch is off.

  2. Take the thermostat off its backplate

    • Time: 1 min

    The thermostat clicks onto the backplate when installed, so pull it straight off.⁠[2]

    You'll know it worked when: The terminal blocks and wires are in view.

  3. Push each wire into the side of its terminal

    • Time: 5 min

    ecobee says the terminal levers should be depressed when the wires are in the right position.⁠[4]

    You'll know it worked when: Each terminal lever is pressed down.

  4. Tug each wire gently

    • Time: 2 min

    A wire that slides out was never seated.⁠[4]

    You'll know it worked when: No wire pulls out of its terminal.

  5. Click the thermostat on and restore power

    • Time: 2 min

    Press it onto the backplate until it clicks, then turn the power back on.⁠[2]

    You'll know it worked when: The screen turns on.

If a wire is too short to reach its terminal, or its end is damaged, stop and call a pro rather than splicing wires in the wall.

Still not fixed? Next likely cause: A single R wire in the wrong terminal

Move a single R wire to Rc

ecobee thermostats have Rc and Rh terminals. ecobee says that if you have only one R wire, whether it is labeled R, Rc or Rh, it goes in the Rc terminal.⁠[5]

  1. Turn off the system power

    • Time: 2 min

    Do this before you move any wire.⁠[3]

    You'll know it worked when: The breaker or switch is off.

  2. Count the R wires on the backplate

    • Time: 1 min

    One R wire labeled R, Rc or Rh means it belongs in Rc.⁠[4]

    You'll know it worked when: You know if you have one R wire or two.

  3. Move it to Rc if it sits in Rh

    • Time: 3 min

    Push it in, tug it, then click the thermostat back on and restore power.⁠[2]

    You'll know it worked when: The single R wire is in Rc and its lever is pressed down.

Two R wires, one in Rc and one in Rh, follow ecobee's dual transformer wiring diagram instead.⁠[5] Leave them in place and see the compatibility section below.

The Smart Thermostat Essential with a Power Extender Kit is the exception. In ecobee's Essential PEK video, the R, Rc or Rh wire goes into the R terminal and the G wire moves to C.⁠[4] Follow the wiring diagram for your model and setup.

Still not fixed? Next likely cause: No C wire, or the Power Extender Kit is miswired

Check the C wire or the Power Extender Kit

The PEK is ecobee's answer for homes with no C wire. It combines the functions of the Y and G wires into a single wire, which frees one wire for the C connection, and it needs at least four wires at the thermostat.⁠[1]

  1. Look for a wire in the C terminal

    • Time: 2 min

    With the power off, check the backplate. No C wire and no PEK means the thermostat has no steady power source.⁠[1]

    You'll know it worked when: You know if the thermostat has a C wire or relies on the PEK.

  2. Confirm the PEK wires sit in the right terminals

    • Time: 10 min

    ecobee says to make sure you inserted the PEK wires into the correct terminals.⁠[3]

    You'll know it worked when: Every PEK wire is in the terminal its wiring diagram shows.

  3. Check the PEK's wire connections are secure

    • Time: 5 min

    ecobee lists secure PEK connections as one of its checks.⁠[6]

    You'll know it worked when: No PEK wire or terminal is loose.

  4. Get a pro for the furnace end of the kit

    • Time: 5 min

    The C wire and the kit both have an equipment end, and checking it means opening the furnace or air handler. ecobee installs the kit at the furnace control board.⁠[1] Take a photo of the thermostat wiring for the technician. ecobee's app asks for one during install so you can refer to it later.⁠[3]

    You'll know it worked when: A technician is booked to check the PEK or C wire at the control board.

If you bought a Smart Thermostat Essential for a home without a C wire, ecobee says the PEK is required for the install.⁠[4]

Still not fixed? Next likely cause: A system the PEK cannot power

When your system is not a fit for the kit

The PEK only works with 24 VAC systems. ecobee lists millivolt systems, high-voltage systems, dual transformer systems, fan coils and communicating units as incompatible.⁠[1] ecobee says its thermostats are compatible with most homes and points to its compatibility checker to confirm.⁠[2]

  1. Run ecobee's compatibility checker

    • Time: 10 min

    ecobee links the checker from each install page.⁠[6]

    You'll know it worked when: You know whether your system suits an ecobee and a PEK.

  2. Leave the wiring as it is

    • Time: 1 min

    If the old thermostat ran an electric baseboard or wall heater, treat the wiring as household voltage and do not touch it.

    You'll know it worked when: Nothing is moved on a system that may be high voltage or millivolt.

  3. Call an HVAC technician or electrician

    • Time: 5 min

    Give them your ecobee model and the wire letters on the old thermostat.⁠[1]

    You'll know it worked when: A pro is booked to confirm the system type and power the thermostat safely.

For the furnace itself, see check the furnace first. If the screen works but the heat does not, see ecobee not turning on the heat.

Still not fixed? See when to call a pro

Parts and tools for this fix

Most fixes here need no parts. A flashlight helps at the breaker panel, and a clean filter is worth having while the cover panel is open.⁠[7]

When to call a pro

Call when the power problem is inside the furnace or air handler, or when your system is one the PEK does not support.

Other smart thermostats have similar power needs; compare Nest thermostat not working, or read how smart thermostats get power.

Frequently asked questions

FAQ

Which ecobee models come with a Power Extender Kit?
All ecobee thermostats except the Smart Thermostat Essential and Smart Thermostat Lite. Those two can use a kit bought separately.⁠[1]
Why did my ecobee go blank after I changed the furnace filter?
The cover panel is the first suspect. ecobee says some systems will not turn on if the panel is not closed properly.⁠[2]
Where does a single R wire go on an ecobee?
In the Rc terminal, whether the wire is labeled R, Rc or Rh.⁠[5]
Can I use the Power Extender Kit on any system?
No. It needs a 24 VAC system and at least four wires at the thermostat, and it does not work with millivolt, high-voltage, dual transformer, fan coil or communicating units.⁠[1]

Sources

  1. ecobee · Manufacturer support

    “Power Extender Kit” · accessed

  2. ecobee · Manufacturer support

    “How to install Smart Thermostat Premium” · accessed

  3. ecobee · Manufacturer support

    “How to install Smart Thermostat Enhanced” · accessed

  4. ecobee · Manufacturer support

    “Installing your Smart Thermostat Essential” · accessed

  5. ecobee · Manufacturer support

    “Installing your ecobee4” · accessed

  6. ecobee · Manufacturer support

    “Installing your ecobee3 lite” · accessed

  7. ENERGY STAR (U.S. EPA) · Government

    “A Guide to Energy-Efficient Heating and Cooling” · PDF · p. 6 (air filter) · accessed

  8. Honeywell Home (Resideo) · Manufacturer support

    “Why won't my thermostat screen power up?” · accessed

  9. Bosch Thermotechnology Corp. · Manufacturer manual

    “Bosch 96% AFUE Gas Furnace BGH96: Installation, Operation & Maintenance Manual” · PDF · §10 p. 39 (door switch), §10.5 p. 41 (24 V wiring, fuse), Fig. 35-36 pp. 42-43, §11.4 p. 44 · accessed

  10. Honeywell Home (Resideo) · Manufacturer support

    “Why is my Heating not Working on my RTH6500WF Smart Series Programmable Thermostat?” · accessed

  11. Google Nest Help · Manufacturer support

    “Troubleshoot a "No power" alert on a Nest thermostat (E298, E448 or M20 help code)” · accessed

ecobee is a trademark of its owner. Before You Call a Pro is not affiliated with or endorsed by ecobee.

How this guide was made

This guide was drafted with AI assistance from the manufacturer and safety sources listed above, then checked against those sources in an AI-assisted review. No licensed technician reviewed it. Last reviewed . Our methodology

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