Article Summary:
If your humidifier doesn’t turn on during a System Test and you get a T08 error, here are a few things you can do to troubleshoot.

To help make sure your system is set up and connected correctly, we created System Test, so you can easily check for any problems during setup, or anytime you need. Below are steps to help you if you get a T08 error during a system test.

How do I test my heating or cooling system?>

Wait a few more minutes

If you can't tell whether or not the humidifier is working, try waiting up to 30 minutes to see if you notice a change in the humidity of your home. The System Test will run for 35 minutes before automatically stopping.

Double check that your humidifier is on and has power

It can be helpful to double check that the system and the breaker connected to the system are on, and that the system has power.

Check to see if heating is on during the test

Some humidifiers are integrated with the heating system, so heating may also turn on when the humidifier is being tested. If your system includes an integrated humidifier, this behavior means that the humidifier is working.

Reseat the wires

Remove the Nest Thermostat display and double check that the humidifier wire is firmly seated in the * connector. Trimming and stripping the ends of the wires can help ensure that they are connecting well.

CAUTION: It's important to protect your thermostat and your system. Turn off power to your system and thermostat at the fuse box before exposing or adjusting any wiring.

Confirm that a professional installed the Nest Thermostat with a relay for your humidifier if needed

It's strongly recommended that a professional install the Nest Thermostat with a humidifier since it may need to be set up differently depending on your system. While Nest has one connector available for humidifiers - the * connector, humidifiers often have two wires. A Nest Pro will add a small relay to your system so that the humidifier will be controlled by a single wire.

How do I set up Nest to work with my whole home humidifier or dehumidifier?>

If the above suggestions don't resolve the issue, there are additional strategies to try in the Troubleshooting tool. You can also contact a Nest Pro using our online finder.