BoilerFaultCodesGlow-worm Red flashing light (Flue) Fault Code
Also written as REDFLASHINGLIGHTFLUE — same fault.
The Glow-worm Red flashing light (Flue) fault code means: your boiler has detected a blockage in the exhaust pipe or a problem with the fan, causing the system to shut down for safety.. It appears on 1 Glow-worm model in our database.
Technical description: Air flow rate safety device: Obstruction of the flue occurs; fan will continue to run but boiler turns OFF.
What causes the Glow-worm Red flashing light (Flue) fault?
This fault occurs when the boiler's safety sensors detect that harmful exhaust gases are not being cleared from the system effectively. The most common reasons are a mechanical failure of the fan, a blockage in the external flue pipe, or a perished internal seal that is leaking air.
This issue can occur during periods of high winds, which may create a back-pressure in the flue that prevents the fan from extracting gases correctly.
DIY fix possible
Check the external flue pipe (the white pipe on your outside wall) for any visible obstructions like bird nests, leaves, or debris.Ensure there are no items such as garden furniture or plants blocking the airway of the flue.If the exterior is clear, do not attempt to open the boiler; you must call a Gas Safe engineer to inspect the internal fan and air pressure switch.
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 Red flashing light (Flue) fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm Red flashing light (Flue) 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