Boiler shows E11, burner stops, and there may be a strong smell of flue gases or evidence of poor combustion.

Safety first: If you smell gas or strong exhaust fumes, turn off the boiler and gas supply immediately and ventilate the area. Do not attempt to adjust gas settings yourself.

Step-by-step checks (user level):

• 1. Check gas supply stability: Confirm other gas appliances work without interruption. If there are supply issues, contact your gas provider.
• 2. Inspect burner and electrodes: With power and gas off, remove the burner cover. Check for soot, rust, or debris on the burner and electrodes. Clean gently with a soft brush and vacuum.
• 3. Check ionisation electrode: Ensure the electrode is correctly positioned in the flame and that the cable is secure and undamaged.
• 4. Reset and observe: Restore power and gas, reset the boiler, and observe operation. If the flame repeatedly goes out and E11 returns, stop using the boiler.

Professional actions: A technician will check inlet gas pressure, burner pressure, combustion quality (CO/CO₂), and adjust or replace components as needed.