What does error code E12 mean on a Google Nest thermostat?

No power to W1 wire. The thermostat isn't detecting power on the W1 (heat) wire.

Can I fix Google Nest code E12 myself?

Start with these safe checks: Make sure the furnace's breaker and service switch are on. With power off, check the W1 wire is fully inserted. If it continues, contact a pro.

When should I call a technician for code E12?

If it continues, contact a pro. Thermostat wiring is low voltage, but switch the HVAC system off at its breaker or service switch before pulling the thermostat off the wall. If the code points to the furnace or outdoor unit, leave gas, combustion and refrigerant parts to a licensed HVAC technician.

Google Nest Thermostat Error Code E12 / E32 / E82: No power to W1 wire

What E12 means

The thermostat isn't detecting power on the W1 (heat) wire.

Also shown as: E32, E82, E162, depending on the model.

Likely causes

Furnace power off
Loose W1 wire

Safe first checks

Make sure the furnace's breaker and service switch are on.
With power off, check the W1 wire is fully inserted.

When to stop

If it continues, contact a pro.

Checked against: Google Nest Help: Troubleshoot Nest thermostat help codes. Codes can differ by model and year, so confirm with your owner's manual.