Ariston Error Codes & Diagnostics
Complete diagnostic directory for official Ariston fault codes. Verify root causes, safe troubleshooting steps, and replacement part numbers before calling a technician.
Ariston Clas overheat codes: the 1-series group and what it points at
Ariston organises Clas fault codes into groups by their leading digit, and the 1-series belongs to the primary water circuit. An overheat entry within that group therefore comes pre-labelled as a water-side condition, which is a genuinely useful piece of structure that most manufacturers do not offer. Applies to: Ariston Clas gas boilers whose fault codes are grouped by leading digit in the Ariston user documentation The grouping described here is the one Ariston uses in Clas user documentation. Ariston sells other ranges with their own conventions, and appliances sold under related brand names are documented separately. Match the code to the manual issued with your own boiler before applying the grouping. Owner-safe checks: Record all three digits of the code exactly, since the leading digit and the pair that follow it do different jobs. | Read the system pressure gauge while the system is cold and write the figure down. | Feel each radiator after a heating attempt and map which heat, which do not, and where the cold begins on the panel. Qualified technician: Anything that restores flow through a sealed heating circuit, from a new circulator to a chemical clean, is Gas Safe registered work when it involves the appliance itself. | A boiler making boiling or knocking sounds should be left off rather than run while waiting, because those episodes deposit scale on the exchanger surface.
Ariston 108 error code: refill request for low system pressure
Ariston shows 108 when the heating circuit pressure has fallen below the level the boiler needs, and it is asking for a refill. The owner opens the filling taps under the boiler until the gauge reads 1.0 to 1.5 bar cold, closes them, then clears the code with the reset control. A drop again within days points at a leak. Applies to: Ariston Clas ONE, Clas System ONE, and Alteas ONE boilers showing 108 This applies to Ariston Clas and Alteas family boilers whose user documentation lists 108 as a filling request. Ariston uses separate codes for a faulty pressure transducer, so if the gauge is already in band and 108 stays, treat it as a sensor branch and call an engineer. Owner-safe checks: With the boiler cold, open both filling taps under the boiler slowly until the gauge reads 1.0 to 1.5 bar, then turn both taps fully off and press reset once. | Note whether 108 clears after the reset and whether the pressure is still in band the next morning. Qualified technician: A pressure that will not hold, 108 showing with the gauge already in band, a suspected transducer fault, or any check inside the boiler casing needs a Gas Safe registered engineer.
Ariston Clas One error 501: no flame detected
On the documented Ariston Clas One family, error 501 is a non-volatile lockout because flame was not detected. The boiler does not restart automatically and the user manual permits reset-button attempts, capped at five within 15 minutes. A returning 501 requires authorised technical service, not continued resetting. Applies to: Clas One and Clas System One condensing gas boilers This definition applies to Clas One and Clas System One user literature linked by Ariston. Nimbus heat pumps, Nuos water heaters, other One-series generations, and regional gas configurations need their own manual. Owner-safe checks: Photograph 501 and the model, check whether other gas appliances operate, and observe sounds only from outside the sealed case. Qualified technician: Gas supply pressure, valve, ignition, burner, flame signal, electrode, grounding, flue, condensate, control, and sealed-case work require authorised qualified service.