High
321 on Worcester Bosch Greenstar 12i System

Your boiler is struggling to perform its automatic safety check to ensure exhaust gases are leaving the house correctly.

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

Self-test of flue gas supervision

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

322View →EAView →CEView →

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