Nest Thermostat Error M31 — What It Means & How to Fix It

What Does This Error Mean?

M31 means your Nest thermostat has gone offline and cannot be reached through the app. Your thermostat is no longer connected to your Wi-Fi network or to Google's servers. You lose remote control through the app, and features like remote schedule changes and energy reports stop working. Importantly, the thermostat itself usually keeps working locally — it still controls your heating and cooling using the last schedule. This is usually a Wi-Fi or network issue, not a hardware failure.

Affected Models

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

Common Causes

Your home's Wi-Fi router lost connection or was restarted and the thermostat did not reconnect
The thermostat moved out of reliable Wi-Fi range due to changes in your home network setup
Your Wi-Fi password was changed and the thermostat still has the old password saved
The thermostat lost power and did not successfully reconnect to Wi-Fi when power was restored
A Google Home or Nest server outage is preventing connection even though your local network is fine

How to Fix It

Check your home's internet connection. Open a webpage on your phone or computer. If the internet is down, fix your router first — the thermostat will reconnect automatically once the network is back.

Unplug your router for 30 seconds and plug it back in. Wait 2 minutes for it to fully restart. Most Nest offline issues resolve themselves once the home network is restored.
Check the Nest app for a Google status banner at the top — this indicates a Google Nest server outage affecting all users. If there is an outage, wait for Google to resolve it.

Google Nest service status is also shown at status.google.com. Server outages are temporary and resolve without any action on your part.
On the thermostat itself, go to Settings > Network. Check whether it shows a Wi-Fi network name. If the field is blank or shows 'Not connected', the thermostat needs to reconnect to your network.

Navigate the thermostat's ring to Settings (the gear icon). Select Network, then select your home Wi-Fi network and enter the password. Make sure you enter the current password if it was recently changed.
Move your Wi-Fi router closer to the thermostat, or add a Wi-Fi extender if the thermostat is far from your router. Check the Wi-Fi signal strength in the thermostat's Network settings.

Nest thermostats need a strong Wi-Fi signal to stay connected reliably. One or two bars of signal can cause frequent drops. Aim for at least three bars for stable connectivity.
As a last resort, perform a factory reset on the thermostat and set it up again from scratch in the Nest app. This clears any corrupted network settings.

Factory reset: go to Settings > Reset > All Settings. You will need to re-add the thermostat in the Nest app and reconfigure your schedule afterward.

When to Call a Professional

M31 almost never requires professional help — it is almost always a network or Wi-Fi issue. Work through the fix steps below before contacting anyone. If the thermostat's screen is completely blank or the thermostat is physically unresponsive, that may indicate a power issue — see error E195 or E24. Contact Google Nest support at home.google.com/support if none of the steps resolve the offline status.

Frequently Asked Questions

Will my heating and cooling still work while Nest is offline?

Yes — in most cases your heating and cooling will continue to work normally while the thermostat is offline. The thermostat runs its saved schedule independently of the internet connection. You just lose the ability to control it remotely through the Nest app. The thermostat's screen and manual controls still work as normal.

My thermostat reconnects but keeps going offline again. What is wrong?

Intermittent offline status usually points to a weak or unstable Wi-Fi signal at the thermostat's location. Check the signal strength in the thermostat's Network settings — anything below two bars will cause frequent disconnects. A Wi-Fi extender or mesh network node placed closer to the thermostat usually resolves this permanently. Also check whether your router is set to 5GHz only — Nest thermostats connect on 2.4GHz, which has longer range.

I changed my Wi-Fi password and now Nest is offline. How do I fix it?

Go to the thermostat's Settings menu using the ring on the device. Select Network, find your home Wi-Fi network in the list, and enter the new password. The thermostat will reconnect and should appear online in the Nest app within a few minutes. In the future, after changing your Wi-Fi password, remember to update any smart home devices — including thermostats, cameras, and doorbells.