On the covered Google Nest thermostat, E157, E158, E194 means the thermostat does not detect an expected wire. Google words E157 as Y1 wire not detected, E158 as W1 wire not detected and E194 as R wire not detected. First, look at the connector named by the code and check that a wire is present and fully inserted.
Differential
Likely causes of “Google Nest thermostat code E157, E158, E194”, and how to tell them apart
- 1
A wire missing from the named terminal
What separates it E157 Y1, E158 W1 or E194 R is shown
How to confirm Check that a wire is present and inserted
- 2
A wire not fully inserted
What separates it The connector button is not down
How to confirm Push the wire in until the button stays down
- 3
Too little or too much bare wire
What separates it About 3/8 inch should be stripped
How to confirm Strip to the right length
- 4
A setup that does not match the wiring
What separates it The diagram does not fit
How to confirm Match the setup wiring diagram
- 5
A wire broken inside the wall
What separates it The connector looks fine
How to confirm Test with another wire
Before you touch a setting
Record this first — changing settings destroys the evidence
- Which code appears
- Which wire it names
- Photograph of the wiring
- The system type
Try in this order
0 of 8 completedWhat to do first
ReversibleLook at the connector named by the code and check that a wire is present and fully inserted.
Correct only the documented fault domain
ReversibleGoogle's wiring steps: turn power off, pull the display, check the named connector holds a fully inserted wire with its button down and about 3/8 inch (6 mm) bare, and that it matches the setup wiring diagram.
Turn off power
ReversibleAt the breaker or system switch.
Pull the display
ReversibleFrom the base.
Look at the named connector
ReversibleIs a wire present?
Check the button is down
ReversibleOn each wire.
Check about 3/8 inch is bare
ReversiblePer Google.
Match the wiring diagram
ReversibleFrom setup.
Model-specific
What is true of this model and not of its siblings
- A named wire
- Each code names a particular wire: Google words E157 as Y1 wire not detected, E158 as W1 wire not detected and E194 as R wire not detected. That means the thermostat expects the wire because of how you set it up, and finds none.
- Google's steps
- Turn power off, pull the display, check the named connector holds a fully inserted wire with its button down and about 3/8 inch (6 mm) bare, and that it matches the setup wiring diagram.
- When wiring changed
- If you changed the system, such as adding air conditioning, rerun setup so the thermostat expects the right wires.
Stop boundary
When this stops being a self-service repair
- !Turn the power off before pulling the display
- !If you are unsure, call an HVAC technician
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does E157, E158, E194 mean on a Google Nest thermostat?+
The thermostat does not detect an expected wire. Google words E157 as Y1 wire not detected, E158 as W1 wire not detected and E194 as R wire not detected.
What do these codes mean?+
The thermostat does not detect an expected wire.
Which wires do they name?+
E157 is Y1, E158 is W1 and E194 is R.
How much bare wire?+
About 3/8 inch.
Is power off necessary?+
Yes, before touching the wires.