BoilerFaultCodesMain 3 Green Flashes Fault Code
Also written as 3GREENFLASHES — same fault.
The Main 3 Green Flashes fault code means: your boiler has briefly lost its flame and is attempting to restart itself automatically.. It appears on 2 Main models in our database.
Technical description: Temporary flame loss – this is a temporary error, the system should reset on its own
What causes the Main 3 Green Flashes fault?
This fault occurs when the boiler's internal sensor fails to detect a consistent flame during operation, leading the system to stop as a safety precaution. The most common reasons include a worn-out sensing probe that can no longer 'see' the flame or a slight instability in the gas supply that prevents a steady burn. It is often a sign that the components responsible for lighting the gas or monitoring the fire are starting to fail.
DIY fix possible
Wait for the boiler to complete its automatic restart cycleCheck that other gas appliances in the home are working correctlyMonitor the boiler to see if the issue persists or clearsPress the reset button if the boiler enters a permanent lockout state
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Main models that show the 3 Green Flashes fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main 3 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