8 03 High

Ariston 8 03 Fault Code

Also written as 803 — same fault.

The Ariston 8 03 fault code means: your boiler has detected that its internal computer settings do not match the physical size of the burner installed, preventing it from starting safely.. It appears on 3 Ariston 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: Mismatch kW Size, ID combustion
Typical repair cost £120-250 (including labour)

Engineer required

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

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Ariston models that show the 8 03 fault code

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

Source

Ariston 8 03 fault code information on this page is sourced and cross-checked against the official Ariston service / installation manuals for each affected model.

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