BoilerFaultCodesAriston A03 Fault Code
The Ariston A03 fault code means: your boiler has shut down because it has detected it is getting too hot, which is usually caused by water not circulating properly through the system.. It appears on 15 Ariston models in our database.
Technical description: The heating flow temperature exceeds 100°C during operation
DIY fix possible
Check that your central heating valves and radiator valves are fully open.Bled your radiators to ensure there is no trapped air blocking the flow.Verify that the boiler pressure is between 1 and 1.5 bar on the pressure gauge.
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Gas Safe Register →Ariston models that show the A03 fault code
Click a model for the full fault code list and model-specific repair notes.
- Bravo 24 MFFI Repair: £120-250
- Challenger 80E Repair: £180-350
- Clas One Repair: £120-250
- E-Combi One Repair: £180-350
- E-Combi One 30 Repair: £180-350
- Egis 24 MFFI Repair: £100-350
- Euro Combi 30 MFFI Repair: £120-250
- Euro Prisma 24 Repair: £120-250
- Genus 24 MFFI Repair: £120-250
- Genus 27 Repair: £150-£350
- Genus 30 Plus Repair: £120-250
- Genus One 24 Repair: £120-250
- Genus One 30 Repair: £120-250
- Genus Premium Repair: £150-£350
- Microsystem 15 Repair: £180-350
Source
Ariston A03 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 27 April 2026