Wiring guide
Heat Pump Thermostat Wiring (6 Wires With C Wire)
The standard modern heat pump: compressor (Y), fan (G), reversing valve (O/B), backup heat (AUX), and power on R and C.
Detected system: Heat pump, 1-stage compressor, 1-stage aux heat, fan, C wire present · 6 wires
Smart thermostat compatibility
| Thermostat | Verdict | What to know |
|---|---|---|
| Nest Learning (4th gen) | Works: direct swap | Direct swap: every wire has a matching terminal. |
| ecobee Premium | Works: direct swap | Direct swap: every wire has a matching terminal. |
| ecobee Enhanced | Works: direct swap | Direct swap: every wire has a matching terminal. |
| Honeywell T9 | Works: direct swap | Direct swap: every wire has a matching terminal. |
| Amazon Smart Thermostat | Works: direct swap | Direct swap: every wire has a matching terminal. |
Where each wire goes, thermostat by thermostat
| Old wire | Nest Learning (4th gen) | ecobee Premium | ecobee Enhanced | Honeywell T9 | Amazon Smart Thermostat |
|---|---|---|---|---|---|
| R (red) | Rc or Rh | Rc | Rc | R | R |
| C (blue) | C | C | C | C | C |
| Y (yellow) | Y | Y1 | Y1 | Y | Y |
| G (green) | G | G | G | G | G |
| O/B (orange) | *OB | O/B | O/B | O/B | O/B |
| AUX (white) | AUX | W1 | W1 | W2 / Aux | W |
Colors are typical, not a rule: always go by the letter the wire was connected to. Click a thermostat for its full diagram, parts and app settings.
How to confirm this is your setup
R, C, Y, G, O/B and AUX: a standard single-stage heat pump with backup heat and a C wire. If there is also a wire on E, see the emergency heat setup instead.
Mistakes to avoid
- Skipping the O/B setting during app setup. The thermostat can’t tell which way your reversing valve works: you have to choose O or B.
- Setting the aux heat lockout too high, so the backup strips run when the heat pump alone could keep up. That costs money.
Our advice
After setup, test in heat mode and in cool mode, and check that the air from the vents changes temperature within a few minutes. If both modes give the same result, the O/B setting is backwards.