High
b18 on Johnson Starley C10d

Your heater has automatically switched off because the air in the vents has become too hot, usually caused by blocked airflow or a lack of ventilation.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Burner blocked due to high duct temperature

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

b19View →E02View →

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