BoilerFaultCodesGlow-worm 03 Fault Code
The Glow-worm 03 fault code means: your boiler has detected an issue with how it moves air and waste gases through the system, causing it to shut down for safety.. It appears on 2 Glow-worm models in our database.
Technical description: Air fault lock
What causes the Glow-worm 03 fault?
This fault occurs when the boiler's internal safety sensors detect that air isn't flowing correctly through the unit to safely remove waste gases. The most common reason is a failing fan that can no longer spin at the required speed or a blockage in the pipes that lead to the outdoors. Because the boiler cannot guarantee that harmful fumes are being moved away safely, it will refuse to ignite as a protective measure.
High winds or extreme stormy weather can occasionally cause this fault by creating back-pressure in the flue pipe that prevents the fan from venting correctly.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Glow-worm models that show the 03 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm 03 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