Can I fix Google Nest code E73 myself?

Start with these safe checks: Make sure the breaker(s) and the service switch for the furnace or air handler are on. With power off at the breaker, pull off the display and check each wire is fully inserted with the connector button down. Check the furnace air filter and replace it if it's dirty. Google says that with these codes in summer you'll likely need an HVAC pro. Drip pan, float switch and fuse checks are inside the equipment; turn power off first or have a pro do it.

When should I call a technician for code E73?

Google says that with these codes in summer you'll likely need an HVAC pro. Drip pan, float switch and fuse checks are inside the equipment; turn power off first or have a pro do it. 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 E73 / E3 / E23: No power to Rc wire

What E73 means

The thermostat isn't detecting power on the Rc wire. In summer, Google says this usually means the HVAC system stopped powering the thermostat.

Also shown as: E3, E23, E195, depending on the model.

Likely causes

HVAC breaker or switch off
Clogged condensate drip pan or drain tripped a float switch
Blown HVAC control board fuse
Loose wire at the thermostat

Safe first checks

Make sure the breaker(s) and the service switch for the furnace or air handler are on.
With power off at the breaker, pull off the display and check each wire is fully inserted with the connector button down.
Check the furnace air filter and replace it if it's dirty.

When to stop

Google says that with these codes in summer you'll likely need an HVAC pro. Drip pan, float switch and fuse checks are inside the equipment; turn power off first or have a pro do it.

Parts that may help

Only order a part once the checks above point to it, and match the part number to your model.

Hayward Manual Air Relief Valve & Pressure Gauge Nut CCX1000N$16.99

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.