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ErrBase

Nest Thermostat Error Codes: E73, E74, E298, W5, N260 Complete Guide

Quick Answer

Nest thermostats (Nest Learning Thermostat, Nest Thermostat E, and Nest Thermostat 2020) display error codes in the Home app and on the device screen. E73 means the thermostat sent a cooling signal but no power was detected on the Y1 wire - the air conditioner did not turn on.

Nest thermostats (Nest Learning Thermostat, Nest Thermostat E, and Nest Thermostat 2020) display error codes in the Home app and on the device screen. E73 means the thermostat sent a cooling signal but no power was detected on the Y1 wire - the air conditioner did not turn on. E74 is the same for heating - the W1 wire did not energize. These are the two most actionable Nest errors because they indicate HVAC system issues, not thermostat faults. E298/E299 mean no power detected at the thermostat at all - the C-wire or power stealing circuit is not providing enough voltage. This is the #1 Nest installation issue and is fixed by adding a C-wire adapter ($25-40). W5 means the Nest sent commands but the HVAC did not respond within the expected time. N260 is a Wi-Fi connectivity loss. The Nest thermostat runs a system test during installation and periodically - error codes appear when these tests fail. Check error history in Google Home app > Thermostat > Settings > Pro Setup.

NestThermostat

About These Nest Thermostat Error Codes

Nest errors: E73 = cooling not responding, E74 = heating not responding, E298 = no power (need C-wire), W5 = HVAC not responding, N260 = Wi-Fi lost. E73/E74 = HVAC issue not thermostat. E298 = add C-wire adapter.

Most Common Error Codes

HVAC system not responding to thermostat signal (E73/E74)40%
No C-wire providing steady power (E298)24%
Blown HVAC fuse or tripped breaker14%
Wi-Fi router changed or moved (N260)12%
Contactor or relay failed in outdoor unit10%

Symptoms You May Notice

  • Error code in Home app or on thermostat screen
  • AC not cooling when called
  • Heat not turning on when called
  • Thermostat display going blank periodically
  • Wi-Fi disconnecting frequently
  • Thermostat battery draining fast

Tools Required for Diagnosis

ScrewdriverMultimeter

How to Identify Your Error Code

1

Check the specific error code in the Google Home app: open the

Check the specific error code in the Google Home app: open the app > select the thermostat > Settings > Pro Setup > Error History. The code tells you exactly which system is affected.

2

For E73 (cooling) or E74 (heating)

3

For E298/E299 (no power)

4

For W5 (HVAC timeout)

Replacement Parts

If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.

Part Name
Nest C-Wire AdapterGoogle C-wire adapter · $25–$40
Nest Thermostat Trim KitGoogle · $15–$20

Repair vs. Replace Calculator

Appliance Age (Years)7 Yrs
Labor Approach
Our Verdict
REPAIR
Estimated Cost: $28 (Parts) vs $250 (New Machine)

Frequently Asked Questions

E73 on Nest but my AC was working yesterday. What happened?
E73 means the cooling signal went out but no response came back. The most common overnight cause: the outdoor AC unit's contactor (a relay that powers the compressor) failed, or the AC circuit breaker tripped from a power surge. Check the breaker first, then listen for a click from the outdoor unit when the Nest calls for cooling.
E298 keeps coming back. Do I need a new thermostat?
No. E298 almost always means insufficient power, not a thermostat defect. Without a C-wire, the Nest relies on power-stealing which is unreliable with certain HVAC systems (especially heat-pump systems and some high-efficiency furnaces). A C-wire adapter ($25-40) permanently fixes E298.
How do I check Nest error history?
Google Home app > select your thermostat > tap the gear icon > Pro Setup > look for error codes or system test results. The Nest also shows recent errors on the device itself: go to Settings > Equipment > Test.
W5 but my furnace has no error lights. What is wrong?
W5 means the Nest waited for the HVAC to respond but it did not start in time. If the furnace has no error codes, check: 1) Is the furnace door switch fully closed? 2) Is the gas valve turned on? 3) Is the condensate drain trap clear (high-efficiency furnaces shut down with a full trap)? 4) Check the wiring at the furnace terminal strip for loose connections.

Models Known to Experience HUB Errors

This repair applies to most Nest thermostats with this error code. Common model numbers include:

Nest Learning Thermostat 3rd Gen, Nest Thermostat E, Nest Thermostat (2020), Nest Learning Thermostat 4th Gen

Last verified for technical accuracy on March 15, 2026