Boiler shows E18, burner stops, sometimes accompanied by gurgling noises.

Safety: Allow the boiler to cool before bleeding air.

• Check pressure: Ensure system pressure is at least 1.0–1.5 bar when cold.
• Bleed boiler and radiators: Use bleed valves to remove trapped air from high points and the boiler’s automatic air vent. Loosen the cap slightly to ensure it can vent.
• Inspect flow sensor: On combi models, check the DHW flow sensor or turbine for debris. Clean or replace if stuck.
• Check pump speed: If the pump has adjustable speed, set it to a higher setting to improve circulation and purge air.
• Reset and test: After bleeding and cleaning, reset the boiler and observe for stable operation without E18.