Google Nest Learning Thermostat 4th Gen Installation And Configuration Manual page 88

Wiring error quick reference guide - Continued
Important Note: These errors may change with future software updates. Visit support.google.com for the
latest information.
Error # Description:
E440 G2 wire detected. Remove W2/AUX wire.
E439 G2 detected. G1 wire is also required.
E442 G3 wire detected. G1 and G2 also required.
E419 Y2 wire without Y1 wire.
E450 AQ and star wire conflict.
E448 No system power.
Reference Material - Wiring Error Quick Reference Guides
What's going on?
The Nest Learning Thermostat is physically
detecting a wire in the W1 connector, a wire in the
AUX/W2 connector, and a G2 (fan) wire in the Y2
connector. This indicates you have more than one
stage of heat and more than one fan speed.
The Nest Learning Thermostat does not support
multiple stages of heat and multiple fan speeds at
the same time.
The Nest Learning Thermostat is physically
detecting a G2 (fan) wire in the Y2 connector, but it's
not detecting a wire in the G connector. Both wires
are required for a multi-speed fan.
The Nest Learning Thermostat is physically
detecting a G3 (fan) wire in the connector, but it isn't
detecting a G2 (fan) wire in the Y2 connector or a
wire in the G connector. All three wires are required
for a three speed fan.
The Nest Learning 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.
The Nest Learning Thermostat has detected a wire in
the AQ connector and a wire in the * connector,
both of which are configured as humidifiers (or
dehumidifiers). The Nest Learning Thermostat
doesn't support connecting 2 humidifiers or 2
dehumidifiers at the same time.
Learning
The Nest
If a C wire is present, then power is not detected on
the C wire. If a C wire is not present, and this is a single
transformer system, then power is neither detected on
Y1 nor on W1, or if this is a dual transformer system,
then power is not detected on Y1.
Thermostat does not detect power.
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