BoilerFaultCodesAriston 3 03 Fault Code
Also written as 303 — same fault.
The Ariston 3 03 fault code means: your boiler's internal computer is experiencing a communication fault, preventing it from safely starting or controlling the heating process.. It appears on 14 Ariston models in our database.
Technical description: Comunication error Main P.C.B. error
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A cover plan would handle faults like 3 03: no call-out fees, no surprise bills.
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Ariston models that show the 3 03 fault code
Click a model for the full fault code list and model-specific repair notes.
- Clas HE 24 Repair: £200-450
- Clas HE 28 Repair: £200-450
- Clas HE 35 Repair: £200-450
- Clas HE Evo Repair: £250-450
- Clas HE R Repair: £250-450
- Clas Net One Repair: £250-450
- Clas System 28 Repair: £250-450
- E-Combi Evo Repair: £200-450
- E-Combi One Repair: £250-450
- E-Combi One 24 Repair: £250-£450
- E-Combi One 30 Repair: £250-450
- Egis Repair: £250-450
- Genus HE Repair: £250-£450
- Microsystem 15 Repair: £250-450
Source
Ariston 3 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