BoilerFaultCodesAriston 3 05 Fault Code
Also written as 305 — same fault.
The Ariston 3 05 fault code means: your boiler has detected an internal communication error with its main control unit, meaning it has shut down as a safety precaution to prevent incorrect operation.. It appears on 14 Ariston models in our database.
Technical description: Main P.C.B. error
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Ariston models that show the 3 05 fault code
Click a model for the full fault code list and model-specific repair notes.
- Challenger 80E Repair: £250-450
- Clas HE 24 Repair: £250-450
- Clas HE 28 Repair: £250-450
- Clas HE 35 Repair: £250-450
- Clas HE Evo Repair: £250-450
- Clas Net One Repair: £250-450
- Clas One Repair: £250-450
- Clas System 28 Repair: £250-450
- E-Combi Evo Repair: £250-450
- E-Combi One Repair: £250-450
- E-Combi One 24 Repair: £280-£450
- E-Combi One 30 Repair: £250-450
- Egis Repair: £250-450
- Microsystem 15 Repair: £250-450
Source
Ariston 3 05 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