Nest Thermostat Error E25 — What It Means & How to Fix It

What Does This Error Mean?

E25 means an internal sensor inside your Nest thermostat has failed. Nest thermostats contain multiple sensors — temperature, humidity, and proximity — to measure your home's environment. When one of these sensors reports a fault or gives readings the system cannot trust, E25 appears. Unlike most Nest errors, E25 is an internal hardware problem — it is not caused by wiring or HVAC issues. In most cases, E25 means the thermostat needs to be replaced.

Affected Models

Nest Learning Thermostat (all generations)
Nest Thermostat E
Nest Thermostat (2020)
Google Nest Thermostat

Common Causes

An internal temperature or humidity sensor has failed due to component aging or a manufacturing defect
Physical damage from a hard knock or impact has damaged the sensor circuitry inside the thermostat
Moisture or condensation has gotten inside the thermostat and damaged internal sensor components
A firmware update did not complete correctly and left the sensor calibration data in a corrupt state
The internal circuit board has developed a fault at the sensor connection point due to age or thermal stress

How to Fix It

Remove the thermostat from its wall base and leave it disconnected for 60 seconds. Reinstall it and allow 2 minutes to restart fully. Check if E25 clears.

A full power cycle clears temporary sensor faults caused by firmware glitches. If E25 is caused by a software issue rather than hardware failure, this may resolve it.
If E25 returns after the power cycle, open the Nest app and check whether a software update is pending. Go to Settings > Software and install any available update.

A failed firmware update can leave sensor calibration data in an inconsistent state. Completing or reinstalling the latest firmware sometimes resolves E25 on its own.
Check whether the thermostat has been exposed to moisture, steam, or direct sunlight for extended periods. These conditions can damage internal sensors over time.

Nests installed near kitchen steam, bathroom humidity, or in direct afternoon sunlight are more vulnerable to internal sensor degradation. Consider moving the thermostat if this applies.
Check your thermostat's warranty status. Go to home.google.com/support and use the serial number on the back of the thermostat to check coverage.

The serial number is printed on a label on the back of the thermostat body — you need to remove it from the wall base to see it. The number is also visible in the Nest app under Settings > Technical Info.
Contact Google Nest support directly. They can run remote diagnostics and confirm whether the thermostat needs replacement. In many cases they will ship a replacement without requiring a service visit.

Google Nest support is available at home.google.com/intl/en_us/support/. Have your thermostat's serial number ready when you contact them.

When to Call a Professional

E25 is a hardware fault inside the thermostat itself — not a wiring or HVAC problem. There is no user-repairable component inside a Nest thermostat. Your first step is to contact Google Nest support — if the device is under warranty, replacement is free. Nest thermostats carry a 2-year limited warranty from Google. If out of warranty, a replacement Nest thermostat costs $100 to $280 depending on the model.

Frequently Asked Questions

Is E25 covered by Google Nest's warranty?

Yes — E25 is an internal hardware failure, and Google's 2-year limited warranty covers hardware defects. If your thermostat is less than 2 years old, contact Google Nest support for a free replacement. Keep your original purchase receipt or order confirmation — Google may ask for proof of purchase date. If you bought the thermostat from a retailer, the purchase date in your email confirmation is sufficient.

Can I keep using my thermostat with E25 showing?

It depends on which sensor has failed. If the temperature sensor is affected, your thermostat cannot accurately measure your home's temperature — heating and cooling will not work correctly. If only the humidity or proximity sensor is affected, basic temperature control may still function. However, we recommend contacting Google support promptly rather than continuing to use a faulty thermostat.

My Nest is out of warranty. Is it worth repairing or should I just replace it?

Nest thermostats are sealed consumer electronics — there is no practical repair option for a failed internal sensor. A replacement Nest Thermostat (2020 model) costs around $100 — comparable to a professional repair attempt. If you are happy with the Nest ecosystem, replacing with a newer model is the practical choice. Alternatively, a basic wired thermostat costs $20 to $60 and does not require a C-wire or Wi-Fi.