5 03 Emergency

Ariston 5 03 Fault Code

Also written as 503 — same fault.

The Ariston 5 03 fault code means: your boiler has detected a flame when it should be turned off, which is a significant safety precaution that prevents the unit from starting until it is inspected.. It appears on 3 Ariston models in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: Flame detected with gas valve closed (After 20 seconds with 502)
Typical repair cost £150-300 (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 5 03 fault code

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

Source

Ariston 5 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