On Flash On High

Potterton On Flash On Fault Code

Also written as ONFLASHON — same fault.

The Potterton On Flash On fault code means: your boiler has stopped working because a sensor that measures water temperature is providing an incorrect reading or has failed, causing the system to shut down for safety.. 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: THERMISTOR
Typical repair cost £120-200 (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 Flash On fault code

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

Source

Potterton On Flash On 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