Installation Manual

Wiring error quick reference guide
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If the Nest Thermostat senses a problem with the wiring, you’ll receive an “E” error. These errors must be fixed
before setup can continue. “N” errors are not as critical and setup will continue but certain features may not
work. “W” errors indicate there is an issue with the Wi-Fi connection.
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“E” errors related to wires not being detected can be the result of a wire not being fully inserted into the
connector or terminal. Ensure all wires are fully inserted and the connector buttons are in the down position
before performing additional troubleshooting.
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Error #
Description:
What’s going on?
E72

- 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.
E73
- No power to Rc wire detected
You’ll see this error if you’ve installed both an Rc wire and The Nest Thermostat
isn’t electrically detecting it.
E74

- No power to Rh wire detected
You’ll see this error if you’ve installed both an Rh wire and The Nest Thermostat
isn’t electrically detecting it.
E75

- No heating or cooling wires detected
- W1 or Y1 wire is required
The Nest Thermostat cannot detect any wires inserted into W1 or Y1. At least
one of these is required.
E77

- Y1 wire not detected. Heat pump
requires a Y1 wire
The 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.
E78

- Additional wire(s) required. AUX/W2
detected by itself
The 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.
E79
- No power to C wire detected
The Nest Thermostat is physically detecting a wire in the C connector, but isn’t
detecting any power to it.
E80

- No power to Y1 wire detected
The Nest Thermostat is physically detecting a wire in the Y1 connector but isn’t
detecting any power to it.
E82
- No power to W1 wire detected
The Nest Thermostat is physically detecting a wire in the W1 connector but
isn’t detecting any power to it.
E83
- Heat pump can have at most one
auxiliary heat wire
The 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.
E84
- Dual fuel requires an alternate heat
wire
The 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.
E85
- Dual fuel can have at most two
alternate heat wires
The Nest Thermostat was set up as a dual fuel system, but the W1, AUX/W2
and * (W3) wires are configured as alternate heat wires.
E86
- Heat pump can have at most one
auxiliary heat wire
 
The Nest Thermostat 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.

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