Can I fix Google Nest code E74 myself?

Start with these safe checks: Check that the HVAC breaker(s) and service switch are on. With power off, check that the Rh wire is fully inserted with the connector button down. If the system breakers are on and the code stays, call an HVAC pro.

When should I call a technician for code E74?

If the system breakers are on and the code stays, call an HVAC 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 E74 / E4 / E24: No power to Rh wire

What E74 means

The thermostat isn't detecting power on the Rh wire. In hot weather, it often means the HVAC system stopped powering the thermostat.

Also shown as: E4, E24, depending on the model.

Likely causes

HVAC power off
Float switch tripped by a clogged drain
Blown HVAC fuse
Loose Rh wire

Safe first checks

Check that the HVAC breaker(s) and service switch are on.
With power off, check that the Rh wire is fully inserted with the connector button down.

When to stop

If the system breakers are on and the code stays, call an HVAC pro.

Checked against: Google Nest Help: Troubleshoot Nest thermostat help codes; Google Nest Help: Troubleshoot thermostat power issues during hot weather (E3, E4, E23, E24, E73, E74, E195). Codes can differ by model and year, so confirm with your owner's manual.