If looking at the display isn’t enough to tell you which thermostat you have, you can also pull off the display and look at the base.

Google T3030EX Nest Learning Thermostat 3rd Generation, White

If you have the manual for your current thermostat (or can find it online), it may describe the function associated with the B connector and help you determine if it’s meant for a heat pump wire or a common wire. If you have both heating and cooling, try to activate both as each component can have separate power switches. There are a few ways to save energy with your thermostat like setting an Eco Temperature when no one’s home, reviewing your Home Report to monitor your energy use, or joining an energy saving program. Nest thermostats also have a star connector * that offers you some flexibility to install specialized systems.Nest thermostats include a few materials to familiarize you with the product and installation, but you should follow the installation instructions in the Nest app which will also provide you with the right wiring diagram for your system. Whether or not there is a wire attached to it, if your thermostat has a separate connector labeled C in addition to a connector labeled B, then the wire in the B connector should be connected to the Nest thermostat’s O/B connector. If your Google Nest thermostat won’t turn on and there'sa blinking red or green light, or no light at all, there could be a power issue or your thermostat may have frozen during a software update.

or reset a Nest thermostat - Google Nest Help Restart or reset a Nest thermostat - Google Nest Help

High voltage thermostats should only be installed or uninstalled by a professional due to the high voltage that they carry. If there's noblinking red light, it's possible that you’ve put wires into the wrong thermostat connectors. Now that you have a picture of the wires connected to the control board, you can use it as a reference to enter wires into the app and help make sure that your wiring diagram is accurate for installation.While most 24 V heating and cooling systems are compatible with Nest thermostats, there are some systems that aren’t compatible. If you moved into a home that already has a Nest thermostat installed, follow these steps to remove the previous owner’s settings.

Nest Thermostats | Central Heating Controls | Screwfix Nest Thermostats | Central Heating Controls | Screwfix

But it will exclude some or all of these wires from the wiring diagram because certain features aren't supported. If you reset Home/Away on your thermostat, everything it has learned about when you're home or away will be reset. You can quickly tell if you have one of these systems without having to use the Compatibility Checker or to look at your thermostat’s wiring. Some countries (such as the UK, France, and The Netherlands) use high voltage wiring for thermostats while others (such as the US and Canada) use low voltage wiring. The Nest thermostat uses its LCD display instead of an indicator light and gets sensor information, like outdoor weather conditions, over Wi-Fi.Google Nest thermostats look similar, and share similar software, but there are some important differences that you’ll need to know for troubleshooting, installation and more. This account disconnection also removes the thermostat from the Home app, so you won't be able to access any control features or settings there. In heat pump systems, the Y2 wire controls the second stage of your compressor, which can help heat or cool your home faster.