Nest Thermostat Error Codes

Nest thermostats are very popular, but they are not insured against breakage. Below there are 3 tables for the 3 models of thermostats of Nest brand. They present fault codes, its description and possible causes of failure of thermostat. Whatever the breakage is (external or internal), this information could help to determine the cause of the problem.

Nest Thermostat Error Codes

Nest Learning Thermostat Error Codes

Error Description:What's going on?
E72- No power wires detected - Rh or Rc wire is requiredYou'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 detectedYou'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 detectedYou'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 requiredThe 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 wireThe 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 itselfThe 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 0/B + Y1 wire.
E79- No power to C wire detectedThe 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 detectedThe 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 detectedThe 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 wireThe 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 wireThe 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 wiresThe 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 wireThe 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.

Nest 3nd Generation Thermostat Error Codes

Error numberDescriptionWhat’s going on?
E42 E51Your 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 N21Power 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 N22Power 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 N23No power to Wlwire detected.Your Nest isn’t electrically detecting your W1 wire, but one is connected to the Nest base.
N4 N24No power to Y1 wire detected.Your Nest isn’t electrically detecting your Y1 wire, but one is connected to the Nest base.
N5 N25No 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 N26No power to G wire detected.Your Nest isn’t electrically detecting your G wire, but one is connected to the Nest base.
N7 N27No power to 0/B wire detected.Your Nest isn’t electrically detecting your 0/B wire, but one is connected to the Nest base.
N28No power to Y2 wire detected.Your Nest isn’t electrically detecting your Y2 wire, but one is connected to the Nest base.
N29No power to wire detected.Your Nest isn’t electrically detecting your wire, but one is connected to the Nest base.

Nest T3007ES Thermostat Error Codes

Error numberDescriptionWhat’s going on?
E1Common 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 E22No 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 E23No 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 E24No power to Rh wire detectedYou’ll see this error if you’ve installed both an Rh wire and Nest isn’t electrically detecting it
E5 E25No 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
E7 E27Y1 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 Ylwire to be attached.
E8 E28Additional wire(s) 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 E29No power to C wire detected.Your Nest is physically detecting a wire in the C connector, but isn’t detecting any power to it.

How I fixed the Nest Thermostat Error E195