ON FLASH FLASH High

Baxi ON FLASH FLASH Fault Code

Also written as ONFLASHFLASH — same fault.

The Baxi ON FLASH FLASH fault code means: your boiler has detected that water isn't moving through the system properly or there isn't enough water inside, causing it to overheat quickly.. It appears on 2 Baxi models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Circulation error or dry fire
Typical repair cost £120-£350 (including labour)

DIY fix possible

Check if your system pressure gauge is too low and top it up if neededEnsure all radiator valves and boiler isolation valves are fully openGently bleed your radiators to remove any trapped air pockets

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Baxi models that show the ON FLASH FLASH fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Baxi ON FLASH FLASH fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026