Nest Thermostat Error E100 — What It Means & How to Fix It

What Does This Error Mean?

The E100 error on your Nest thermostat means the device cannot connect to your Wi-Fi network. Without Wi-Fi, you can still control the thermostat at the device itself — but you lose remote control, scheduling, and energy reports through the Nest app. This is usually caused by a Wi-Fi password change, a router issue, or the thermostat moving out of range.

Affected Models

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

Common Causes

Your Wi-Fi password was changed but the Nest was not updated with the new password
Your Wi-Fi router was replaced or reset, changing the network name or password
The Nest thermostat is too far from the router and the signal is too weak
Your router is temporarily offline or experiencing issues
The Nest needs a software update to resolve a Wi-Fi compatibility issue

How to Fix It

Restart your Wi-Fi router. Unplug it from power for 30 seconds, plug it back in, and wait 2 minutes for it to fully restart. Then check if the Nest automatically reconnects.

A router restart is the fastest first step. The Nest will usually reconnect automatically within 3 to 5 minutes of the router coming back online.
Update the Wi-Fi password on your Nest. On the thermostat display, press the ring and go to Settings > Network > Add Network (or select your existing network). Re-enter the current Wi-Fi password.

This is the most common fix when E100 started after you changed your Wi-Fi password or got a new router.
Check your Wi-Fi signal strength at the thermostat's location. In the Nest app, go to your thermostat > Settings > Technical Info and look at the RSSI value. Aim for -70 dBm or better (closer to 0 is stronger).

If the signal is weak (below -80 dBm), the thermostat is too far from the router. Move the router closer or add a Wi-Fi extender.
Check if your router is blocking the Nest. Some routers have device filtering or parental controls that can block new or unfamiliar devices. Log into your router's admin page and check the blocked devices list.

The Nest's MAC address can be found at Settings > Technical Info > MAC Address on the thermostat itself.
If the Nest still cannot connect, try connecting it to a 2.4 GHz network instead of 5 GHz. On dual-band routers, the 2.4 GHz band has better range. Look for a network name that says '2.4G' or check your router settings.

The Nest Thermostat (2020) only supports 2.4 GHz Wi-Fi. Other Nest models support both bands, but 2.4 GHz is more reliable at longer distances.

When to Call a Professional

E100 is almost always fixable without professional help. If your Nest consistently cannot maintain a Wi-Fi connection even when the router is close by, contact Google Nest support at home.google.com/support. A hardware fault with the Nest's Wi-Fi radio is rare but possible.

Frequently Asked Questions

Can I still use Nest without Wi-Fi?

Yes. Without Wi-Fi, the Nest thermostat works as a standard thermostat — you can set the temperature and schedule directly on the device. However, you lose all remote control features, the Nest app access, energy history, automatic software updates, and integration with Google Home or Amazon Alexa. Reconnecting to Wi-Fi restores all these features.

Does Nest support 5 GHz Wi-Fi?

It depends on the model. The Nest Thermostat (2020) — Google's most affordable model — only supports 2.4 GHz Wi-Fi. The Nest Learning Thermostat (3rd and 4th Gen) and Nest Thermostat E support both 2.4 GHz and 5 GHz. If you are not sure which model you have, check the back of the device or your original packaging.

Why does the Nest keep disconnecting from Wi-Fi?

Intermittent disconnections are usually caused by a borderline Wi-Fi signal — strong enough to connect but not strong enough to stay connected reliably. Other causes include router firmware bugs, network congestion, or a router that is too aggressive about disconnecting idle devices. Enabling 'keep-alive' settings on your router or adding a Wi-Fi extender near the thermostat usually resolves recurring E100 errors.