High Lockout
Simultaneous 1 Slow / 1 Fast on Glow-worm Hideaway 40B

Your boiler is failing to start because its internal safety checks haven't confirmed that the fan is pushing waste gases out of the flue 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

Lighting Sequence-Fan/APS / Check connection & operation

What causes this fault?

This fault occurs when the boiler's safety system detects that the fan isn't moving enough air to safely expel exhaust gases. The most common reasons are a seized fan motor, a faulty air pressure switch that fails to signal the control board, or small tubes becoming blocked with debris or moisture. Without confirming a clear airflow, the boiler will refuse to ignite to prevent a buildup of dangerous fumes.

This issue is more frequent during the first cold spell of autumn, as fan bearings can seize up after sitting idle throughout the summer months.

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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