On On Flash High

Potterton On On Flash Fault Code

Also written as ONONFLASH — same fault.

The Potterton On On Flash fault code means: your boiler's internal electronic brain has detected a critical error and is unable to safely control the heating system, meaning the boiler has shut down.. It appears on 4 Potterton 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: PCB Fault - Replace PCB.
Typical repair cost £250-400 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Potterton models that show the On On Flash fault code

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

Source

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

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026