Bosch water heater displays E2 and shuts down shortly after ignition attempt

Safety first: Disconnect power and close the gas valve before opening the unit. Allow the heater to cool.

• Verify ground connection: Ensure the heater is properly grounded. Check the green/yellow ground wire at the junction box and chassis. Tighten any loose screws.
• Clean burner and flame rod: Remove the burner assembly if accessible per the service manual. Use compressed air to blow dust and debris from the burner and orifices. Clean the flame sensor rod with fine abrasive pad to remove oxidation.
• Check gas pressure (pro only): Inadequate gas pressure can cause weak flame. A licensed technician should measure inlet and manifold gas pressure with a manometer and adjust or correct supply issues.
• Inspect wiring harness: Look for loose or corroded connectors between the flame sensor and control board. Reseat connectors firmly.
• Persistent E2: If cleaning and grounding checks do not resolve the issue, the flame sensor or main control board may be defective and require replacement by a professional.