Troubleshooting when a Nest Temperature Sensor isn't in a good spot

You’ll see a M12 error typically because your temperature sensor is placed in an area that’s much colder or hotter than where your thermostat is installed. For instance: Near a heating vent, stove, hot water pipe Next to a window in direct sunlight In a poorly insulated room or on a poorly insulated wall In a drafty area, near a door to the outside Too high or too low in a room In a room that isn’t heated or cooled by your system, such as your basement, porch, or garage Outside of the zone the thermostat is controlling, if you have a system with 2 or more thermostats

If your sensor is in a room that’s a lot colder than the rest of your home, your system may overheat other rooms and make them uncomfortable.

Try the following steps to troubleshoot the error message. The most important step is to move your sensor to a new place as instructed in step one. Try a few different locations first, and if the message still doesn’t go away, try the other steps. The error message should disappear soon after you’ve fixed the issue.

1. Move your sensor

Moving your sensor is often the best solution, but it doesn’t have to be very far. In some cases, you’ll only have to move it a couple of feet.

• Make sure your sensor isn’t near any of the things listed in the “What causes an M12 error message” section above: heat sources, uninsulated rooms, etc.


• Ideally, it should be installed about chest height. Lower or higher may cause your system to overheat or overcool the room and the rest of your home.


• If the temperature difference between the room where your sensor is located and the rest of your home is very large, try moving it to another room.


• Move your sensor to another room if you placed it in a room that isn’t heated or cooled by your system, such as your basement, porch, or garage.


• If you have a zoned system with 2 or more thermostats, make sure that all sensors are placed in the same zone as the thermostat they’re connected to.

2. Change your scheduled target temperature

Tweaking your thermostat’s scheduled temperatures a couple of degrees can also help alleviate the issue in some cases, but may not solve it. Try reducing a heating temperature (or increasing a cooling temperature) by just a couple of degrees to see if the error goes away.

How to change your thermostat’s temperature schedule >

3. Change your sensor’s schedule

Changing when your temperature sensor is active can sometimes help. For instance, if you live in a warm climate and the sensor is in a bedroom with many large windows, it may be better to use your thermostat’s built-in sensors during the day to adjust cooling and use the sensor in the bedroom during the evening when the sun is down.

How to change your temperature sensor’s schedule >

4. Have a Nest Pro check your system

In some cases, your system may not be performing as well as it should and will have to work harder to keep your home comfortable. You can contact a Nest Pro in your area to check your system’s air filter, ventilation ducts, and general functioning.