Wiring error quick reference guide
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.
“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.
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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