Nest Smart Thermostats Error Codes

E1

Nest thermostat displays E1 and cannot connect to the Wi‑Fi network

Wi‑Fi Radio or Network Authentication Fault

E10

Nest thermostat shows E10 and reports that it cannot detect the R wire or power from the HVAC system

No 24V Power on R Terminal

E11

Nest thermostat displays E11 and reports a problem with the fan (G) wire or fan control

Indoor Blower Fan Call Circuit Fault (G)

E12

Nest thermostat shows E12 and reports a problem with the O/B wire or heat pump reversing valve

Heat Pump Reversing Valve Control Fault (O/B)

E13

Nest thermostat displays E13 and reports a problem with the W2/Aux wire or second‑stage heat/aux heat

Second‑Stage or Auxiliary Heat Call Fault (W2/Aux)

E15

Nest thermostat shows E15 and reports that it has detected a serious power issue and has shut down to protect itself

Overvoltage / Short Circuit Protection Event

E195

Nest thermostat shows E195 and reports that it is shutting down due to power issues, often during peak cooling or heating

Intermittent Power Drop / Brownout Protection

E2

Nest thermostat shows E2 and reports a sensor error or temperature reading failure

Internal Temperature/Humidity Sensor Failure

E20

Nest thermostat displays E20 and reports that it has detected a problem with the C wire or power to the device

Common Wire Power Stability Fault

E294

Nest thermostat displays E294 and reports that it cannot detect the R wire or that the R wire is misconfigured

R Wire Configuration / Detection Fault

E3

Nest thermostat displays E3 and cannot detect the outdoor temperature or weather data

External Weather Data / Internet Service Fault

E4

Nest thermostat shows E4 and reports that it is not receiving enough power from the HVAC system

Insufficient Power / Low Voltage on Rc/Rh and C

E5

Nest thermostat displays E5 and reports a power or R wire issue, often after calling for heating or cooling

R Wire Power Interruption / Blown HVAC Control Fuse

E6

Nest thermostat shows E6 and reports a wiring error or incompatible wiring configuration

Thermostat Terminal Miswiring / Incompatible System Type

E7

Nest thermostat displays E7 and reports a C wire or power sharing issue

Common Wire Detection / Power Sharing Fault

E73

Nest thermostat shows E73 and reports no power to the Rc wire (cooling system)

Loss of 24V Power to Cooling Circuit (Rc)

E74

Nest thermostat displays E74 and reports no power to the Y1 wire (cooling call)

Open Cooling Call Circuit (Y1 to Condenser)

E8

Nest thermostat shows E8 and reports a problem with the Y1 wire or cooling system

Compressor Call Circuit Fault (Y1)

E9

Nest thermostat displays E9 and reports a problem with the W1 wire or heating system

Heat Call Circuit Fault (W1)

N1

Nest thermostat shows N1 and cannot connect to the Nest service or app, even though Wi‑Fi appears connected

Cloud Service / Nest Account Connectivity Fault

N2

Nest thermostat shows N2 and cannot find or join the selected Wi‑Fi network

Wi‑Fi Association / Authentication Failure

N3

Nest thermostat shows N3 and frequently disconnects from Wi‑Fi or cannot maintain a stable connection

Unstable Wi‑Fi Link / Signal Degradation

N4

Nest thermostat shows N4 and cannot connect to the Nest service after a router or ISP change

Router / ISP Compatibility or Configuration Fault

Symptom

Nest thermostat base plate is loose or thermostat does not sit securely on the wall

Mechanical Mounting / Base Plate Misalignment

Symptom

Nest thermostat calls for cooling but air conditioner does not start

Open Cooling Call Circuit or Condenser Lockout

Symptom

Nest thermostat calls for heat but furnace does not start

Open Heat Call Circuit or Furnace Lockout

Symptom

Nest thermostat cannot be added to the Nest or Google Home app (pairing fails)

Bluetooth / Setup Radio or Account Pairing Fault

Symptom

Nest thermostat cannot control humidifier or dehumidifier accessory

Accessory Control Output Fault

Symptom

Nest thermostat causes short cycling: HVAC turns on and off frequently

Short Cycling Due to Control or System Issues

Symptom

Nest thermostat display is completely blank and unresponsive

No Power / Depleted Internal Battery

Symptom

Nest thermostat display is very dim or backlight does not turn on

Display Backlight / Ambient Light Sensor Fault

Symptom

Nest thermostat does not detect motion and does not wake up or follow occupancy schedule

Occupancy Sensor / Proximity Sensor Failure

Symptom

Nest thermostat frequently overshoots the set temperature (room gets too hot or too cold)

Control Algorithm / Anticipator Misbehavior

Symptom

Nest thermostat is hot to the touch or feels unusually warm

Overheating of Thermostat Electronics

Symptom

Nest thermostat loses time or schedule when power is interrupted

Internal Backup / Battery Retention Failure

Symptom

Nest thermostat reboots randomly or frequently restarts during heating or cooling

Intermittent Power Drop / Firmware Instability

Symptom

Nest thermostat shows cooling, but only the fan runs and no cold air comes out

Fan Only Operation / Compressor Not Running

Symptom

Nest thermostat shows heating, but only the fan runs and no warm air comes out

Fan Only Operation / Failed Ignition or Heat Source

Symptom

Nest thermostat shows incorrect room temperature compared to other thermometers

Temperature Sensing / Calibration Error

Symptom

Nest thermostat wiring terminals do not clamp or hold wires securely

Terminal Spring Clamp Failure