BoilerFaultCodesMain 5 Red Flashes Fault Code
Also written as 5REDFLASHES — same fault.
The Main 5 Red Flashes fault code means: your boiler's internal memory chip has developed a software or connection error, meaning it can no longer remember its correct settings to operate.. It appears on 2 Main models in our database.
Technical description: Parameter storage unit (PSU) error
What causes the Main 5 Red Flashes fault?
This fault occurs when the boiler's internal memory chip fails to communicate with the main control board, similar to a corrupted file on a computer. It is usually caused by a hardware failure within the chip itself or a loose physical connection on the circuit board that prevents the boiler from reading its essential operating instructions. Because the boiler no longer knows its own safety limits or settings, it shuts down immediately as a precaution.
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 5 Red Flashes fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main 5 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