Thermostat displays E19 and indicates an internal sensor self-test failure at startup.

Safety first: Turn off power before removing the thermostat.

Steps to attempt:

• 1. Full power reset: Isolate power for at least 5 minutes, then restore and observe if E19 reappears.
• 2. Check environment: Ensure the thermostat is not exposed to condensation or water leaks that could damage electronics.
• 3. Firmware reload (if supported): Use the Baxi app or service tools to reload firmware if the option exists.

When to call a professional: Persistent E19 indicates internal hardware failure; replacement of the thermostat is required.