8 (Diagnostic) High

Potterton 8 (Diagnostic) Fault Code

Also written as 8DIAGNOSTIC — same fault.

The Potterton 8 (Diagnostic) fault code means: your boiler has detected a faulty sensor that monitors the internal water levels, causing it to shut down to prevent potential overheating.. It appears on 1 Potterton model 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: Dry fire sensor Sensor failed open or closed circuit Replace sensor
Typical repair cost £150-250 (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 8 (Diagnostic) fault code

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

Source

Potterton 8 (Diagnostic) 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 27 April 2026