BoilerFaultCodesMain FLASH OFF ON Fault Code
Also written as FLASHOFFON — same fault.
The Main FLASH OFF ON fault code means: your boiler has got too hot and has shut itself down as a safety precaution to prevent damage.. It appears on 1 Main model in our database.
Technical description: Overheat lockout
DIY fix possible
Check that all radiator valves are fully open to allow water to circulateEnsure your system pressure is topped up to between 1 and 1.5 barTurn the selector switch to the reset position for five seconds and then back to heat/hot water
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like FLASH OFF ON: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Main models that show the FLASH OFF ON fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Main FLASH OFF ON 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