ecobee Premium Wiring Diagram: C Wire, PEK+ and Heat Pumps

1. The 12 terminals

ecobee’s Premium diagrams show two rows on the backplate. The left row is G, C, Y1, Y2, PEK+ and OB. The right row is Rc, Rh, W1, W2, ACC+ and ACC−.

One detail trips people up. The Premium manual says its installation photos show the older Smart Thermostat with Voice, and that the same connections apply with minor layout changes. It also says the PEK terminal is now labeled PEK+. If your backplate doesn’t match a photo, go by the terminal letters. The same manual rates the thermostat for 24 VAC at 2 A at most, and says not to connect it to line voltage or millivolt systems.

2. The four wiring diagrams as a table

This table reads across diagrams 1 to 4 in the manual’s wiring section. The left column is the thermostat terminal. Each cell is the wire that lands there, named by its old label. Y2 and W2 apply only if your system has second stages, and the diagrams draw them as dashed optional wires.

With a PEK, only R, G, Y and W pass through the kit. In the diagrams, Y2, W2 and O/B run straight from the thermostat to the equipment, so each one needs its own wire in the cable. ecobee’s install page links these diagrams as separate PDFs, plus one for dual-transformer systems.

3. Wiring with a C wire, step by step

These steps follow Scenario 1 in the manual. The ecobee app also builds a diagram for your wires, so install it first.

1. Turn off power at the master switch or breaker. Confirm by calling for heat or cooling and checking that no air comes from the vents after a few minutes.
2. Remove the old cover and photograph the wiring.
3. Check for a hidden C wire. A spare wire tucked into the wall can work if it connects to C at the control board. ecobee notes that a C wire may also be labeled X or B. Our multimeter guide shows how to test it.
4. Label each wire with the supplied labels and disconnect one at a time. Leave any jumper between R terminals on the old thermostat.
5. Mount the backplate, with the trim plate if you need it. ecobee specifies a 3/16 inch bit for the anchors.
6. Insert each wire into the side of its terminal, not the front. Pressing the lever makes this easier, and it lowers when the wire is held. Tug each wire gently.
7. Push extra wire back and seal the wall hole, since drafts can affect temperature readings.
8. Restore power and press the thermostat on until it clicks. With 24 VAC present, the light bar flashes green before it powers on, and the install page says the screen shows Hi.

Before you start, check that your wires match a setup we cover, such as the 5-wire setup with a C wire. Spare wires can be taped off and tucked into the wall.

4. No C wire: installing the PEK

ecobee’s PEK support article says the kit combines Y and G onto one wire, which frees a wire to act as C. You need at least four wires at the thermostat. With the power off:

1. Open the furnace or air handler and photograph the control board.
2. Compare wire colors. If they differ from the colors at the thermostat, there is a splice, and ecobee says the PEK goes at the splice instead.
3. Label the R, G, Y (or Y1) and W (or W1) wires that run to the thermostat. If a terminal holds more than one wire, label only the thermostat wire.
4. Move those four wires from the board to the matching gray terminals on the PEK.
5. Connect the PEK’s five white wires to R, C, G, Y and W on the board. Leave the outdoor unit’s wires on C and Y, because ecobee says they must stay connected.
6. Mount the PEK without straining the wires, and close the cover fully. ecobee notes that some systems won’t turn on with the panel loose.
7. At the thermostat, connect:
   • R wire to Rc
   • G wire to C
   • Y wire to PEK+
   • W wire to W1
8. Restore power and follow the setup on screen.

ecobee’s support article lists “R wire to the R terminal” for the Premium, while its install page and diagrams use Rc, which is the Premium’s label. Our no C wire guide compares the options if the PEK won’t suit your system.

5. Heat pumps: O/B and backup heat

The manual gives these rules, and the heat pump diagram matches them:

• Y1 runs the compressor, and Y2 runs a second compressor stage.
• O/B runs the reversing valve. A lone wire labeled B goes on OB, but ecobee warns it may actually be a common wire.
• AUX, AUX1 or a heat pump’s W2 wire normally goes on W1, and AUX2 goes on W2.
• E normally goes on W1.
• Separate O and B wires: ecobee recommends booking a professional.

The Premium supports up to four heat stages on a heat pump: two compressor and two auxiliary. Setup applies these steps when it detects an O/B wire, or when you select one. Our O/B terminal page covers the O and B difference, and the aux heat vs emergency heat guide explains why one terminal can serve both.

6. Systems that need something else

• Heat-only with two or three wires: the PEK doesn’t apply. The manual’s diagrams 8 and 9 use a Fast-Stat Common-Maker.
• Two transformers: wires on both Rc and Rh stay on their own terminals with no jumper. The PEK isn’t compatible, so you need a real C wire.
• W3 or Y3 wires: ecobee thermostats don’t support a third furnace or cooling stage. The manual lists workarounds at the control board.
• Humidifier, dehumidifier or ventilator: the manual shows a 1-wire accessory on ACC+, and a 2-wire accessory on ACC+ and ACC−. You can add one accessory.
• Terminals marked 1 2 3 4 or A B C D: ecobee calls these proprietary systems. Look further to see if the equipment also has R, C, W, Y and G terminals, and expect to lose some proprietary features if it does.
• L1, L2 or 110 to 240 V labels: this is high voltage, which ecobee thermostats can’t run. See our line voltage guide.

The manual has no dual fuel diagram, so confirm that setup with ecobee’s compatibility checker or the app. If you have the Enhanced instead, use its own diagrams, which show a shared W2/OB terminal.

7. If it doesn’t work after wiring

The install page lists four checks when the thermostat won’t turn on:

1. Every wire is fully seated in its terminal.
2. The HVAC cover panel is closed.
3. A single R wire is in Rc.
4. If you used the PEK, its wires are secure and in the right terminals.

If the screen shows the wrong wires during setup, the manual gives two choices: power off and fix the wiring, or, if you are sure the wiring is right, tap the undetected wire’s terminal to set it by hand. After setup, go to Menu, Settings, Equipment, Wiring to see what the thermostat detects, and use Re-configure Equipment to change it. Our wire not detected guide covers loose or damaged wires, and the troubleshooting guide covers the furnace side. Before heating or cooling starts, the manual says calibration can take up to 20 minutes.

8. Frequently asked questions