Nest Thermostat Error E45 — What It Means & How to Fix It

What Does This Error Mean?

Error E45 on your Nest thermostat indicates a problem with the thermostat's internal temperature or humidity sensor. The Nest uses these sensors to measure your home's current temperature and make smart adjustments. When the sensor fails or reads an impossible value, the Nest displays E45 and may not be able to control your temperature correctly.

Affected Models

Nest Learning Thermostat (2nd, 3rd gen)
Nest Thermostat E
Nest Thermostat (2020 model)
Google Nest Thermostat

Common Causes

The Nest thermostat has been exposed to extreme temperatures or humidity that damaged the sensor
Condensation inside the thermostat has affected the sensor readings
The thermostat is located near a heat source, vent, or exterior wall that skews its readings
The thermostat display has developed an internal hardware fault
Dust or debris inside the thermostat is affecting sensor performance

How to Fix It

Remove the Nest display from its base and leave it off for 10 minutes to allow it to acclimate to room temperature.

Extreme temperature changes (like placing the Nest near an exterior door in cold weather) can temporarily throw off the internal sensor.
Reattach the display and go to Settings > Reset > Restart.

A software restart can clear a temporary sensor error.
Check the thermostat's location. Is it near a kitchen vent, a sunny window, a drafty exterior door, or a lamp? All of these can cause abnormal readings.

The Nest should be on an interior wall, 4–5 feet from the floor, away from direct heat or cold sources.
Gently clean around the vents on the thermostat with a soft, dry brush to remove any dust buildup.

The temperature and humidity sensor ports are the small vents/holes on the side of the thermostat display.
If E45 persists and the thermostat is within warranty, contact Google Nest support at support.google.com/googlenest for a replacement.

Nest thermostats have a 2-year limited warranty from the purchase date.

When to Call a Professional

If restarting and relocating the thermostat does not resolve E45, the thermostat display may need to be replaced. Contact Google Nest support to check warranty options. A replacement Nest thermostat display (without the base) is available from Google.

Frequently Asked Questions

Can the Nest still control my HVAC with E45?

It depends on the severity of the sensor fault. If the sensor is completely failed, the Nest may not be able to read the room temperature at all and will stop controlling your system. A partially working sensor may allow operation but with reduced accuracy.

Does E45 mean my entire Nest needs replacing?

Not necessarily the entire unit. The Nest thermostat consists of two parts: the display (which contains the sensors and screen) and the base (which connects to your wiring). In many cases, replacing just the display resolves sensor-related errors. Contact Nest support to confirm.

Why would condensation get inside my Nest thermostat?

Condensation can form inside a thermostat if the HVAC system produces a lot of cold air and the thermostat is in a location with high humidity. This is more common in very humid climates or if the thermostat is positioned near a supply vent blowing cold air directly on it.