How to turn the power off to your system

You should always turn off the power before you connect or disconnect any wires from your Google Nest thermostat, and you should test to make sure that the power is off. This helps protect you and your equipment during installation or troubleshooting.

1. Locate where your system switch is

To turn the power off, you'll first need to find the switch that controls power to the heating and cooling equipment in your home. There are two general types of power switches for heating and cooling systems:

Some systems will be turned on and off by a
switch in your breaker or fuse box. The
system switch or fuse can be labeled HVAC,
heating, furnace, or something similar.
If your breaker box isn't labeled, or you can't
find the power switches for your system, you
can switch the main breaker or remove the
main fuse. This will turn off all power in your
home.

Turn off power through breaker box or switch

Important: Doing this can affect other electronics in your home. After you turn power back on, you may need to reset the time on clocks and check other devices that are plugged in.

Other systems are turned on and off by a switch that's directly connected to the system. These often look like a regular light switch, but don't control any lights.

Note: If you have a dual transformer system with both heating and cooling, there may be separate switches for heating and cooling.

2. Turn off power

Flip the switch or remove the fuse to turn off power to your system. Remember to turn off both switches if your dual transformer system has separate switches for heating and cooling.

Nest Learning Thermostat (4th gen) has an illuminated level on the base plate under the display. To check if the thermostat has power, remove the display and check if the level illuminates. If the LED remains off, it is not receiving power. Verify that the LED is off on the base plate.

3. Test that you've correctly turned off power

Always check to make sure that you've turned off your system. To check that your system's power is off, you'll change the temperature on your thermostat by at least 5 degrees.

If it's winter, turn up the temperature to turn on heating.
If it's summer and you have system cooling, turn down the temperature to activate your central air conditioning.
Wait at least 5 minutes and check if your system turns on. You'll need to wait because many systems have a built-in delay. You can listen for your system to turn on, or put your hand near an air vent to feel if there's warm or cool air coming through.

Troubleshooting

If your thermostat is off

Your system may be off as well. Your thermostat probably doesn't have an internal battery that will let it control your system when power is off.
Nest thermostats (and many other thermostats) have an internal battery that keeps them working for a bit even if they're not receiving power.

If your system turns on during the test

The switches on your breaker or fuse box may be mislabeled. Try another switch and repeat the test.
The breaker switch may not have been fully pushed to the off position. Try flipping it on and back off again using more force.

4. Turn the power back on

When you're done with thermostat wiring, you can turn the power to your system back on. You can confirm it's on by running the tests in step 3 and waiting for your system to turn on.

Nest Learning Thermostat (4th gen) only: Verify that the LED is illuminated on the base plate.

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