Boiler shows E11; may indicate earth leakage or insulation fault on heating elements.

Safety first: Immediately isolate the boiler from the mains. Earth leakage can present a serious electric shock risk.

• Visual inspection: With power off, inspect the heating element terminals and wiring for signs of moisture, corrosion, or damaged insulation.
• Check for water leaks: Look for any leaks around the element gaskets or nearby pipework that could be wetting electrical components.
• Insulation resistance test (qualified persons only): Use a megohmmeter to test insulation resistance between each element terminal and earth. Values significantly below manufacturer recommendations (often <1 MΩ) indicate a failing element.
• Drying (temporary measure only): If moisture is suspected and insulation readings are borderline, the boiler may be left isolated to dry, but this is not a permanent fix. The source of moisture must be eliminated.
• Replace faulty element/wiring: Any element or cable with poor insulation must be replaced. After repair, re-test insulation resistance before reconnecting power.

Warning: Do not bypass earth leakage protection or operate the boiler with known insulation faults.