E6
Nest
Thermostat Terminal Miswiring / Incompatible System Type
Nest thermostat shows E6 and reports a wiring error or incompatible wiring configuration
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Heat pump wired as conventional system or vice versa, W1/W2/Y/Y2/O/B wires on wrong terminals, High‑voltage (120/240V) wires incorrectly connected to Nest base, Shared common wire mis‑terminated causing cross‑shorts
How to Fix / Troubleshooting
Safety: If you see thick wires with wire nuts or 120/240V cables behind the old thermostat, stop and call a professional. Nest thermostats are only for low‑voltage (24V) systems.
- Verify system type: Confirm whether your system is a heat pump or conventional furnace/AC. Check the old thermostat labels or HVAC documentation.
- Match wire labels: Use the photo of your old thermostat wiring (if available) and the Nest compatibility checker. Ensure each conductor is on the correct Nest terminal (e.g., O/B for heat pump reversing valve, W1 for heat, Y1 for compressor).
- Remove unused jumpers: If your old thermostat had metal jumpers between R and Rc/Rh, do not recreate them on the Nest. Nest internally handles Rc/Rh.
- Check for high‑voltage: If any wire measures 120V or 240V to ground with a multimeter, do not connect it to Nest. This indicates an incompatible line‑voltage system.
- Re‑seat all wires: Remove and reinsert each wire into the correct Nest terminal, ensuring 3–4 mm of bare copper is inserted and clamped.
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Repair Difficulty
Medium
3/5
Required Part
Thermostat Low‑Voltage Wiring Harness
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