Nest thermostat · Status lights
What a blinking light on a Nest thermostat means
Sources checked · how we check
Which light you see depends on which Nest thermostat you have. On the Nest Thermostat E and the Learning Thermostat up to 3rd gen, green means it is busy and red means the battery is low and charging. The 4th-gen Learning Thermostat shows a dark yellow light for the same low battery. Either way, a light that keeps coming back after the thermostat has been working is telling you something else.
What this covers
Google documents these lights per model. The tables below name the models each one covers. The battery-powered Nest Thermostat, the 2020 model with a touch bar on the right side, has no light codes: Google's advice when it will not turn on is to reseat or replace its two AAA batteries. Where a Nest system uses a Heat Link box, the Heat Link has its own lights, documented separately.
Source: Google: troubleshoot when your thermostat won't turn on
Nest Thermostat E and Nest Learning Thermostat (3rd gen or earlier)
Blinking green
The thermostat is updating its software, starting up or restarting. Google says this normally lasts a minute or two.
What to do: Wait. If it is still blinking green and unresponsive after 15 minutes, Google says it may have frozen during the update: pull the display straight off the base and push it back on until it clicks.
Source: Google: troubleshoot when your thermostat won't turn on
Blinking red
The battery charge is very low and it is charging. Google says to wait until it is fully charged before using it to control heating or cooling, which can take several minutes or up to an hour.
What to do: On a new install, wait, or speed it up by charging the display from a wall charger over USB, never a computer's USB port. If the light appears after the thermostat has been in regular use, or keeps coming back, Google says there may be a wiring or power problem: check the power readings under Settings > Technical Info > Power. Wiring runs to your heating system, so if you are not certain, that part is a job for a heating engineer.
Source: Google: troubleshoot when your thermostat won't turn on
No light, and it will not turn on
Google lists this with the other two: it can be a power issue, or the thermostat frozen during a software update.
What to do: Check the display is fully seated on the base, then that the system's breaker or switch is on and its fuse is not blown. If the problem is in the system or its wiring, Google points to a local professional.
Source: Google: troubleshoot when your thermostat won't turn on
Nest Learning Thermostat (4th gen)
Dark yellow
The battery charge is very low and it is charging. Google says charging can take several minutes or up to an hour.
What to do: Wait until it has fully charged before using it to control heating or cooling. If the yellow light appears after regular use, or keeps coming back, Google says there may be a wiring or power problem: check the power readings under Settings > Technical Info > Power, and contact a professional if the system needs servicing.
Source: Google: troubleshoot when your thermostat won't turn on
No light, and it will not turn on
The battery has drained, which Google says means not enough power is reaching it over the system's wires.
What to do: Check the display is fully seated on the base, then that the system's breaker or switch is on and its fuse is not blown.
Source: Google: troubleshoot when your thermostat won't turn on
If none of these match your light
A Nest thermostat also shows numbered help codes on screen, which are documented separately from the light. Where a system uses a Heat Link box, the Heat Link has its own status, heating and hot water lights, and each Heat Link model uses them differently: on the Heat Link for the Nest Thermostat E, for example, blinking yellow means something needs attention on the thermostat. If the light you are looking at is on the Heat Link, Google's Heat Link article is the one to read.
Frequently asked questions
Why is my Nest thermostat blinking green?
On a Nest Thermostat E or a Learning Thermostat up to 3rd gen, it is updating, starting up or restarting, and Google says that normally takes a minute or two. If it is still blinking and unresponsive after 15 minutes, it may have frozen mid-update: remove the display and reconnect it.
Why is my Nest thermostat blinking red?
On a Nest Thermostat E or a Learning Thermostat up to 3rd gen, the battery is very low and charging. Wait for it to finish, up to about an hour. If a red light keeps returning on a thermostat that has been working normally, Google says that points to a wiring or power problem rather than a flat battery.
What does the yellow light on a Nest thermostat mean?
On the 4th-gen Nest Learning Thermostat, a dark yellow light means the battery is very low and charging. If the light is on a Heat Link box rather than the thermostat, it means something different: check the thermostat screen for an error code.
Should I keep using the thermostat while it is charging?
Google says to wait until it has fully charged before using it to control your heating or cooling.