Google's offline article says a Nest thermostat that is offline cannot connect to your home wifi, so you cannot control it from the app and some features are unavailable, but you can still set the temperature on the thermostat itself. Most steps need you to be at home with access to the thermostat, router and modem. Its power article adds that the thermostat may disconnect from wifi if it is not getting power from the heating and cooling system, even if the battery reads fine, and a low battery also makes it disconnect to save power.
The checks in more detail
So check power first: does the display work and is there a low battery or No power message? Then restart the router and modem, move or restart the thermostat with Settings, Restart, and check the wifi password and network. Google's Wi-Fi and connection article for Nest products lists steps for signal and router settings. The steps differ for the Nest Learning Thermostat (4th gen), the Nest Thermostat and older models, so choose yours in the article. If your wifi name, password or router changed, use Google's new wifi guide to reconnect the thermostat, which may need the device to be reset in some cases.
If the display is blank, use the won't turn on article instead. For heating and cooling operation without the app, use the thermostat's ring or buttons directly. Photograph the display and the app message and write down when it went offline, since the pattern tells you whether it is a power fault or a wifi fault. A thermostat that goes offline only in very hot or cold weather may be reacting to the load on the system, so note the outdoor temperature. Contact support with the model, software version and the display message ready.
If the thermostat is offline right after a heating season starts, the system's first cold-start load can briefly disturb the wifi, so give it a full day and check power before you rebuild the connection. On the Nest Learning Thermostat 4th gen you can lift the display off its baseplate to check whether the baseplate light comes on, which Google notes stays dark when the thermostat is not receiving power, and that quick check separates a power fault from a wifi fault before you spend an hour on the router.
Differential
Likely causes of “Nest thermostats is offline or unavailable”, and how to tell them apart
- 1
A power problem
What separates it The thermostat is offline with a No power alert because the system is not giving it power
How to confirm Fix the C wire or fit a Power Connector, so the thermostat receives steady power
- 2
A low battery
What separates it The thermostat disconnects to save power because its battery is low
How to confirm Change or charge the battery, and then check whether the thermostat reconnects
- 3
A wifi change
What separates it The thermostat went offline after you changed the router or the wifi password
How to confirm Reconnect it to the new network, using the wifi settings on the thermostat
- 4
A weak signal
What separates it The thermostat drops off often because the wifi signal at its position is weak
How to confirm Improve the signal, by moving the router closer or adding a mesh point near the thermostat
- 5
A stuck state
What separates it The thermostat is unresponsive because it is stuck in a bad state
How to confirm Restart it from the settings menu, which keeps all of your settings
Before you touch a setting
Record this first — changing settings destroys the evidence
- The exact message shown on the thermostat's display
- Any change made to the router or the wifi
Try in this order
0 of 7 completedCheck power and battery
ReversibleCheck the power and the battery, since the display and its alerts show which one is the problem.
Restart router and modem
ReversibleRestart the router and the modem, and wait for all their lights to settle before you test.
Restart the thermostat
ReversibleRestart the thermostat from its settings menu, which keeps your settings and often clears the problem.
Check wifi name and password
ReversibleCheck the wifi name and the password, and retype the password carefully, since it is case sensitive.
Reconnect to the network
ReversibleReconnect the thermostat to the network, using the change wifi option in its settings menu.
Move the router closer
ReversibleMove the router closer, or improve the signal, if the thermostat is far from the router.
Contact Google
ReversibleContact Google if it stays offline, and tell them the model and the message on the display.
Model-specific
What is true of this model and not of its siblings
- Learning Thermostat 4th gen
- Has a rechargeable battery charged over USB.
- Nest Thermostat
- Uses replaceable batteries as backup.
Stop boundary
When this stops being a self-service repair
- !If the thermostat stays offline after a restart and reconnect, contact Google Nest support
- !If there is a No power alert, check the wiring
- !If you are unsure about wires, contact an HVAC pro
Evidence ledger
Sources behind this answer
Offline steps by model.
No power alerts, C wire and Power Connector.
Wifi and connection.
Changing wifi.
The company and its products.
Exact questions
Common questions
Can I still control it when offline?+
Yes, you can still control it at the thermostat itself, though the app cannot reach it.
Why does it go offline with good battery?+
It can go offline with a good battery when the heating system does not supply power.
Which article for a blank screen?+
Google has a separate article for a screen that will not turn on at all.
Do steps differ by model?+
Yes, the steps differ by model, so check the article for your own thermostat.
Do I need to be home?+
You need to be at home for most steps, since they are done at the thermostat.
Can a router change cause it?+
Yes, a change of router or password can make the thermostat lose its connection.
Should I restart first?+
Yes, restart it first, since a restart keeps all of your settings and fixes many problems.
Which app do I use for the Nest Learning Thermostat?+
You use the Google Home app, and the Nest app for older devices, to change the temperature, schedules and settings.
How does the thermostat update?+
It updates automatically over wifi, and manual updates are not offered, so a thermostat that is offline cannot update.