BoilerFaultCodesMain 5 Green Flashes Fault Code
Also written as 5GREENFLASHES — same fault.
The Main 5 Green Flashes fault code means: your boiler has experienced a temporary electronic communication glitch and is attempting to sort itself out automatically.. It appears on 2 Main models in our database.
Technical description: Parameter error on parameter storage unit (PSU) or printed circuit board (PCB) – this is a temporary error, the system should reset on its own.
What causes the Main 5 Green Flashes fault?
This fault occurs when the boiler's internal computer brain momentarily misses a heartbeat while communicating with its memory chip. It is usually caused by a minor electrical interference or a brief data glitch within the electronic control system. In most cases, the boiler identifies the mismatch itself and corrects the data error without any mechanical failure.
DIY fix possible
Wait for the boiler to complete its automatic reset processIf the flashing continues for more than 15 minutes, turn the selector switch to 'Reset' for five secondsMonitor the boiler to see if the lights return to a steady green
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Main models that show the 5 Green Flashes fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main 5 Green 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