BoilerFaultCodesAriston 3 04 Fault Code
Also written as 304 — same fault.
The Ariston 3 04 fault code means: your boiler has detected that the reset button has been pressed too many times in a short period, which has triggered a built-in safety lockout to prevent potential damage to the electronic control board.. It appears on 13 Ariston models in our database.
Technical description: Too many (> 5) resets in 15 minutes / 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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Search the official register for a qualified engineer in your area.
Gas Safe Register →Ariston models that show the 3 04 fault code
Click a model for the full fault code list and model-specific repair notes.
- Challenger 80E Repair: £200-450
- Clas HE 24 Repair: £150-350
- Clas HE 28 Repair: £150-350
- Clas HE 35 Repair: £150-350
- Clas HE Evo Repair: £100-250
- Clas Net One Repair: £90-180
- Clas One Repair: £90-180
- E-Combi Evo Repair: £90-£150
- E-Combi One Repair: £200-450
- E-Combi One 24 Repair: £0-120
- E-Combi One 30 Repair: £200-450
- Egis Repair: £100-200
- Microsystem 15 Repair: £200-450
Source
Ariston 3 04 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