Installation Manual
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?
E155
No heating or cooling detected. W1 or
Y1 wire is required
The Nest thermostat isn't physically detecting a W1 (heating) or Y1 (cooling)
wire. One of these wires is required for any type of system that the Nest
thermostat supports.
E157
Y1 wire not detected
The Nest thermostat isn't physically detecting a Y1 wire or one isn't
attached. A wire in your */OB terminal is configured as a Heat Pump
O/B wire. Heat Pumps require a Y1 wire to function.
E158
Y1 wire not detected
The Nest thermostat isn't physically detecting a W1 wire or one isn't
attached. A wire in the */OB terminal is configured as a second stage
of heat. Your Nest thermostat needs a first stage of heat (W1) to use a
second stage of heat.
E159
No power to C wire detected
The Nest thermostat is physically detecting a wire in the C (common)
connector but isn't detecting any power to it.
E160
No power to Y1 wire detected
The Nest thermostat is physically detecting a wire in the Y1 (cooling)
connector but isn't detecting any power to it.
E162
No power to W1 wire detected
The Nest thermostat is physically detecting a wire in the W1 (heating)
connector but isn't detecting any power to it.
E164
Dual fuel requires an alternate heat
wire
The Nest thermostat was previously set up as a dual fuel system, but
it's not detecting a W1. One of these wires is required in order to have
alternate heat.
E169
Y2 wire without Y1 wire
The Nest thermostat is detecting a Y2 wire but not a Y1 wire. Both
wires are required for 2 stage conventional cooling systems.
E182
E183
E184
E188
The Nest thermostat has an
overcurrent error
The Nest thermostat may be wired incorrectly, or the system may be
incompatible. If using a C wire, ensure it is connected to the
Thermostat’s C terminal.
E194
R wire not detected
The Nest thermostat isn't physically detecting the R wire or one isn't
attached. An R wire must be connected for your Nest thermostat to
work.
E195
No power to R wire detected
The Nest thermostat physically detects the R wire, but doesn't detect
any power. If you've just installed the Nest thermostat, check to make
sure you turned the breaker back on after installation.
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