BoilerFaultCodesMain 4 Red Flashes Fault Code
Also written as 4REDFLASHES — same fault.
The Main 4 Red Flashes fault code means: your boiler has detected an issue with the ventilation fan, which means it cannot safely clear exhaust fumes and will not ignite.. It appears on 2 Main models in our database.
Technical description: Fan Fault
What causes the Main 4 Red Flashes fault?
This fault occurs when the boiler's control system senses that the fan is not spinning at the correct speed to safely expel waste gases. The most common reasons are a mechanical failure of the fan motor itself, a loose connection in the wiring, or a fault on the main circuit board that prevents power from reaching the fan.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Main models that show the 4 Red Flashes fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main 4 Red Flashes fault code information on this page is sourced and cross-checked against the official Main service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026