Bosch EasyControl displays error C3 and the thermostat cannot complete initial setup or loses configuration.

Safety first: Do not open the EasyControl main unit; there are no user-serviceable internal components. Work only with external wiring and power.

• 1. Check power stability: Ensure the EasyControl is powered from a stable 230 V supply via its original Bosch EasyControl power supply module or boiler bus. Avoid shared circuits with heavy loads that cause voltage dips.
• 2. Reboot the device: Turn off power to the EasyControl for at least 60 seconds, then restore power and wait for the boot sequence to complete. Observe if C3 reappears.
• 3. Verify firmware via app: Open the Bosch EasyControl app, connect to the thermostat, and check for firmware updates. If an update is available, follow the on-screen instructions and ensure power and Wi‑Fi remain stable during the process.
• 4. Reset configuration (last resort): From the EasyControl installer menu, perform a factory reset only after noting all heating curves, schedules, and device pairings. Re-run the setup wizard.

Professional help: If C3 persists after a clean power cycle and firmware update, the internal memory or processor may be defective. Contact Bosch support for warranty evaluation or replacement of the EasyControl main unit.