Thermostat display shows E0 and will not control heating or cooling

Safety first: Turn off power to the HVAC system at the breaker panel before removing the thermostat from the wall or accessing any wiring.

Steps to try:

• Power cycle the thermostat: Turn off the HVAC breaker for 2–3 minutes, then turn it back on. Wait for the thermostat to reboot and see if E0 clears.
• Check for firmware update: Using the American Standard Home app or web portal (if supported by your model), check if a firmware update is pending. Apply the update and allow the thermostat to restart.
• Factory reset: From the thermostat menu, navigate to Settings → Reset → Factory Reset (wording may vary). Reconfigure Wi‑Fi, system type, and schedules after reset.
• Inspect the sub-base and pins: With power off, gently pull the thermostat off the wall sub-base. Inspect the connector pins for bent or corroded contacts. Reseat the thermostat firmly on the sub-base.

When to call a technician: If E0 persists after reset and power cycling, the internal control board may be defective and the thermostat should be replaced.