| E1 | Common wire C required. | This wiring error may appear after installation when Nest can’t get power while the system is turned on. Nest’s software should be updated if this error appears |
| E2 E22 | No power wires detected. Rh or Rc wire is required. | You’ll see this error when either a Rh or Rc wire was not installed or the Rh or Rc wire that was installed isn’t powered. |
| E3 E23 | No power to Rewire detected. | You’ll see this error if you’ve installed both an Rc wire and Nest isn’t electrically detecting it. |
| E4 E24 | You’ll see this error if you’ve installed both an Rh wire and Nest isn’t electrically detecting it |
| E5 E25 | No heating or cooling wires detected. | Nest cannot detect any wires inserted into W1 or Y1. At least one of these is required. |
| W1 or Y1 wire is required | |
| E6 | Too many wires detected. | This error indicates that the wiring combination you’ve installed is no supported by Nest. Verify the actual wiring for the system and remove at least one of 0/B, W1, Y1 or AUX wires as appropriate. |
| E7 E27 | Y1 wire not detected. Heat pump requires a Y1 wire. | Your Nest is physically detecting a wire in the 0/B connector. This connector is exclusively used for heat pumps which also require a Y1 wire to be attached. |
| E8 E28 | Additional wire(s)l required. AUX/W2 detected by itself. | Your Nest is physically detecting a wire in the AUX/W2 connector. Supported configurations that use this connector also include a W1 wire or an 0/B + Y1 wire. |
| E9 E29 | No power to C wire detected. | Your Nest is physically detecting a wire in the C connector, but isn’t detecting any power to it. |
| E10 E30 | No power to Y1 wire detected. | Your Nest is physically detecting a wire in the Y1 connector but isn’t detecting any power to it. |
| E11 | Heat pump wireO/B detected. No heat pump system present. | Your Nest 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’s software. |
| E13 E33 | Heat pump can have at most one auxiliary heat wire. | Your Nest 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. |
| E34 | Dual fuel requires an alternate heat wire. | Your Nest 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. |
| E35 | Dual fuel can have at most two alternate heat wires. | Your Nest was setup as a dual fuel system, but the W1, AUX/W2 and * (W3) wires are configured as alternate heat wires. |
| E36 | Heat pump can have at most one auxiliary heat wire. | Your Nest was previously setup as a single fuel system with auxiliary heat, but it’s detecting W1, AUX/W2 and * (W3) wires that aren’t supported in that configuration. |
| E37 | Your Nest was previously setup as a single fuel system with auxiliary heat, but it’s detecting W1 and * (W3) wires that aren’t supported in that configuration. |
| E38 | Your Nest was previously setup as a single fuel system with auxiliary heat, but it’s detecting AUX/W2 and * (W3) wires that aren’t supported in that configuration. |
| E42 E51 | Your Nest may have tripped an internal fuse and Nest needs to be replaced. | Your Nest either has wires that aren't fully inserted into the connectors or has tripped an internal fuse. |
| N1 N21 | Power wire Rc detected. Not connected to equipment. | Your Nest isn’t electrically detecting your Rc wire, but one is connected to the Nest base. |
| N2 N22 | Power wire Rh detected. Not connected to equipment. | Your Nest isn’t electrically detecting your Rh wire, but one is connected to the Nest base. |
| N3 N23 | No power to Wlwire detected. | Your Nest isn’t electrically detecting your W1 wire, but one is connected to the Nest base. |
| N4 N24 | No power to Y1 wire detected. | Your Nest isn’t electrically detecting your Y1 wire, but one is connected to the Nest base. |
| N5 N25 | No power to AUX/W2 wire detected. | Your Nest isn’t electrically detecting your AUX/W2 wire, but one is connected to the Nest base. |
| N6 N26 | No power to G wire detected. | Your Nest isn’t electrically detecting your G wire, but one is connected to the Nest base. |
| N7 N27 | No power to 0/B wire detected. | Your Nest isn’t electrically detecting your 0/B wire, but one is connected to the Nest base. |
| W2 | Failed to connect. | Your Wi-Fi access point may have security settings enabled that prevent your Nest from connecting. |
| W3 | Your Wi-Fi access point is not providing a network IP address to your Nest. |
| W4 | Nest is connected to your wireless network but not to the internet. |
