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What do the Nest Learning Thermostat's error codes mean?

The Nest Learning Thermostat will present an error if it detects a problem with the wires connected to its base or with the Internet connection. This article describes what they mean and provides tools to get them resolved.

Errors that begin with an E or an N are related to problems the Nest Learning Thermostat finds with your wiring. Errors that begin with W are related to your Wi-Fi connection.

During setup, the Nest Thermostat will detect the wires that are connected to the base and uses System Match to configure its software for your type of system. If the Nest Thermostat finds a problem during wire detection, the Nest Thermostat will show a diagram of the wires highlighting where the problem might be.

Press the ring to see a report with an error code. Some wiring errors arise when a necessary wire isn’t physically detected in the Nest Thermostat's connector. Other errors occur when a wire is connected to the Nest Thermostat base, but it doesn’t seem to be connected to your heating and cooling system on the other end. The Wi-Fi errors come up when the Nest Thermostat is having trouble connecting to the Internet.

Below are descriptions of each error, along with a link to our Troubleshooting tool to walk you through isolating the error and suggest steps you can take to get it fixed right now.

ERROR CODE ERROR MESSAGE WHAT'S GOING ON

E1

Common wire C required.

You may need to update your Nest Thermostat's software or attach a common wire.

Troubleshoot an E1 error

E2 & E22

No power wires detected. Rh or Rc wires required.

The Nest Thermostat isn’t physically detecting your Rc or Rh wire or one isn’t attached.

Troubleshoot an E2 error

Troubleshoot an E22 error

E3 & E23

No power to Rc wire detected.

The Nest Thermostat isn’t electrically detecting your Rc wire.

Troubleshoot an E3 error

Troubleshoot an E23 error

E4 & E24

No power to Rh wire detected.

The Nest Thermostat isn’t electrically detecting your Rh wire.

Troubleshoot an E4 error

Troubleshoot an E24 error

E5 & E25

No heating or cooling detected. W1 or Y1 wire is required.

The Nest Thermostat isn’t physically detecting your a W1 or Y1 wire. One of these wires is required for any type of system that the Nest Thermostat supports.

Troubleshoot an E5 error

Troubleshoot an E25 error

E6

Too many wires detected. Please remove at least one of O/B, W1, Y1 or AUX.

The Nest Thermostat doesn’t support the configuration or wires you’ve attached.

Troubleshoot an E6 error

E7 & E27

Y1 wire not detected. Heat pump requires a Y1 wire.

Your Nest Thermostat is physically detecting a wire in the O/B connector. This connector is exclusively used for heat pumps which also require a Y1 wire to be attached.

Troubleshoot an E7 error

Troubleshoot an E27 error

E8 & E28

Additional wire(s) required. AUX/W2 detected by itself.

Your Nest Thermostat is physically detecting a wire in the AUX/W2 connector. Supported configurations that use this connector also include a W1 wire or an O/B + Y1 wire.

Troubleshoot an E8 error

Troubleshoot an E28 error

E9 & E29

No power to C wire detected.

Your Nest Thermostat is physically detecting a wire in the C connector but isn’t detecting any power to it.

Troubleshoot an E9 error

Troubleshoot an E29 error

E10 & E30

No power to Y1 wire detected.

Your Nest Thermostat is physically detecting a wire in the Y1 connector but isn’t detecting any power to it.

Troubleshoot an E10 error

Troubleshoot an E30 error

E11

Heat pump wire O/B detected. No heat pump system present.

Your Nest Thermostat is physically detecting a wire in the O/B connector but isn’t detecting any power to it. You may need to update your Nest Thermostat's software.

Troubleshoot an E11 error

E13 & E33

Heat pump can have at most one auxiliary heat wire.

Your Nest Thermostat was previously setup as a single fuel system with auxiliary heat put it’s detecting both W1 and AUX/W2 wires that aren’t supported in that configuration.

Troubleshoot an E13 error

Troubleshoot an E33 error

E34

Dual fuel requires an alternate heat wire.

Your Nest Thermostat was previously setup as a dual fuel system but it’s not detecting a W1, AUX/W2 or (W3) wire that is required to have alternate heat.

Troubleshoot an E34 error

E35

Dual fuel can have at most two alternate heat wires.

Your Nest Thermostat was setup as a dual fuel system, but the W1, AUX/W2 and (W3) wires are configured as alternate heat wires.

Troubleshoot an E35 error

E36

Heat pump can have at most one auxiliary heat wire.

Your Nest Thermostat was previously setup as a single fuel system with auxiliary heat put it’s detecting, W1, AUX/W2 and (W3) wires that aren’t supported in that configuration.

Troubleshoot an E36 error

E37

Heat pump can have at most one auxiliary heat wire.

Your Nest Thermostat was previously setup as a single fuel system with auxiliary heat put it’s detecting, W1 and (W3) wires that aren’t supported in that configuration.

Troubleshoot an E37 error

E38

Heat pump can have at most one auxiliary heat wire.

Your Nest Thermostat was previously setup as a single fuel system with auxiliary heat put it’s detecting AUX/W2 and (W3) wires that aren’t supported in that configuration.

Troubleshoot an E38 error

E39

Y2 wire without Y1 wire.

Your Nest Thermostat is physically detecting a Y2 wire but not a Y1 wire that is required for 2 stage conventional cooling systems or 2 stage heat pumps.

Troubleshoot an E39 error

E40

W3 wire without W2/AUX wire.

Your Nest Thermostat is physically detecting a (W3) wire but not a W2/AUX wire that is required for 3 stage conventional heating systems.

Troubleshoot an E40 error

E41

E wire without O/B wire.

Your Nest Thermostat is physically detecting a (E) wire but not an O/B wire. O/B is a heat pump wire and the Nest Thermostat only supports the use of emergency heat with heat pump systems.

Troubleshoot an E41 error

E42 - E51

Your Nest Thermostat may have tripped an internal fuse and the Nest Thermostat needs to be replaced.

Your Nest Thermostat either has wires that aren't fully inserted into the connectors or has tripped an internal fuse.

Troubleshoot the error

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ERROR CODE ERROR MESSAGE WHAT'S GOING ON

N1 & N21

Power wire Rc detected. Not connected to equipment.

Your Nest Thermostat isn’t electrically detecting your Rc wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N1 error

Troubleshoot a N21 error

N2 & N22

Power wire Rh detected. Not connected to equipment.

Your Nest Thermostat isn’t electrically detecting your Rh wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N1 error

Troubleshoot a N21 error

N3 & N23

No power to W1 wire detected.

Your Nest Thermostat isn’t electrically detecting your W1 wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N3 error

Troubleshoot a N23 error

N4 & N24

No power to Y1 wire detected.

Your Nest Thermostat isn’t electrically detecting your Y1 wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N4 error

Troubleshoot a N24 error

N5 & N25

No power to AUX/W2 wire detected.

Your Nest Thermostat isn’t electrically detecting your AUX/W2 wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N5 error

Troubleshoot a N25 error

N6 & N26

No power to G wire detected.

Your Nest Thermostat isn’t electrically detecting your G wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N6 error

Troubleshoot a N26 error

N7 & N27

No power to O/B wire detected.

Your Nest Thermostat isn’t electrically detecting your O/B wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N7 error

Troubleshoot a N27 error

N8 & N28

No power to Y2 wire detected.

Your Nest Thermostat isn’t electrically detecting your Y2 wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N8 error

Troubleshoot a N28 error

N9 & N29

No power to wire detected.

Your Nest Thermostat isn’t electrically detecting your wire, but one is connected to the Nest Thermostat base.

Troubleshoot a N9 error

Troubleshoot a N29 error

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ERROR CODE ERROR MESSAGE WHAT'S GOING ON

W1

The Nest Thermostat can’t continue to connect to your Wi-Fi network.

Your Wi-Fi access point may now fully support a Wi-Fi standard known as power saving mode.

Troubleshoot a W1 error

W2

Failed to connect.

Your Wi-Fi access point may have security settings enabled that prevent your Nest Thermostat from connecting.

Troubleshoot a W2 error

W3

Failed to connect.

Your Wi-Fi access point is not providing a network IP address to your Nest Thermostat.

Troubleshoot a W3 error

W4

Failed to connect.

The Nest Thermostat is connected to your wireless network but not to the internet.

Troubleshoot a W4 error

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