Bosch tankless water heater powers on but does not ignite; display shows E0

Safety first: Turn OFF power at the breaker and close the gas shutoff valve before removing any covers. Allow the unit to cool completely.

• Check model and gas type: Verify the heater model and that it is installed for the correct gas type (Natural Gas vs LP). Compare with the rating plate on the front or side of the unit.
• Inspect DIP switches: Remove the front cover. Locate the main control board and its DIP switches. Using the installation manual for your exact Bosch model (e.g., Therm 520, Greentherm, Tronic), confirm each DIP switch position matches your gas type, altitude, and vent configuration.
• Reset configuration: If any DIP switch is incorrect, set it to the proper position. Restore power and attempt a reset by turning the unit OFF and ON or using the reset button if provided.
• Factory reset (if supported): Some Bosch electronic models allow a parameter reset via button sequence. Follow the service manual instructions to clear configuration errors.
• When to call a pro: If E0 persists after verifying DIP switches and gas type, the control board parameters may be corrupted and the electronic control module may need replacement by a qualified technician.