BoilerFaultCodesGlow-worm Fast Flashing (8Hz) Fault Code
Also written as FASTFLASHING8HZ — same fault.
The Glow-worm Fast Flashing (8Hz) fault code means: your boiler has detected an internal electrical error or a component failure during its startup sequence that is preventing it from firing up.. It appears on 1 Glow-worm model in our database.
Technical description: Sequence Error / Software Error / Ignition Lockout
What causes the Glow-worm Fast Flashing (8Hz) fault?
This fault occurs when the boiler's internal computer performs a safety check during startup and detects a conflict between the fan and the air pressure sensor. The most common reason is that the control board is receiving incorrect electrical signals, or a vital component has physically failed and is preventing the ignition sequence from completing.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Glow-worm models that show the Fast Flashing (8Hz) fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm Fast Flashing (8Hz) fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026