Ariston boiler — Ariston Clas ONE, Clas System ONE, and Alteas ONE boilers showing 108 Error Codes Directory

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.