BoilerFaultCodesMain 4 Green Flashes Fault Code
Also written as 4GREENFLASHES — same fault.
The Main 4 Green Flashes fault code means: your boiler is temporarily struggling to talk to its internal control parts and is trying to reconnect itself.. It appears on 2 Main models in our database.
Technical description: Communication error between printed circuit board (PCB) and Control – this is a temporary error, the system should reset on its own
What causes the Main 4 Green Flashes fault?
This fault occurs when the boiler's main control board loses its digital connection with the internal display or user interface components. It is often caused by a brief dip in power or electrical interference that prevents these parts from sharing data correctly. In most cases, it is a hardware 'stutter' rather than a permanent mechanical breakage.
DIY fix possible
Wait up to 10 minutes to see if the error clears itself as designedTurn the selector switch to 'Reset' for 5 seconds and then back to its original positionSwitch the main electrical power to the boiler off and back on again
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Main models that show the 4 Green Flashes fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main 4 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