Boiler indicates E23, flue gas recirculation or CO₂ too high detected by safety system (where fitted).

Safety first: High CO₂ or flue gas recirculation is dangerous. Switch off the boiler and ventilate the area.

• Inspect flue terminal: Ensure the flue outlet and air intake (for concentric systems) are correctly spaced and not obstructed.
• Check room ventilation: For open combustion appliances, verify that ventilation openings are not blocked and that no powerful extract fans are creating negative pressure.
• Clean burner components: Remove and clean the burner head, mixing plate, and air intake grilles.
• Combustion analysis: Have a technician perform a flue gas analysis and adjust the burner to Weishaupt settings.

When to call a professional: Any combustion-related fault should be checked by an authorised Weishaupt service engineer.