BoilerFaultCodesGlow-worm APS neon lit Fault Code
Also written as APSNEONLIT — same fault.
The Glow-worm APS neon lit fault code means: your boiler has detected an issue with the airflow system, which is preventing the burner from lighting for safety reasons.. It appears on 1 Glow-worm model in our database.
Technical description: Air Pressure Switch neon status. If not lit, check fan and 240V supply to fan.
What causes the Glow-worm APS neon lit fault?
This fault occurs when the boiler's safety sensors cannot confirm that the fan is successfully pushing exhaust fumes out of the flue. The most common reasons are a buildup of debris in the fan or air tubes, or the mechanical switch itself failing to register the flow of air. Until the boiler is certain it can vent gases safely, it will prevent the burner from firing.
This issue is frequently seen during periods of high wind, which can create back-pressure in the flue that interferes with the sensitive air pressure switch.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Glow-worm models that show the APS neon lit fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm APS neon lit 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 27 April 2026