BoilerFaultCodesAriston 109 Fault Code
The Ariston 109 fault code means: your boiler has too much water pressure inside the system, causing it to shut down for safety.. It appears on 6 Ariston models in our database.
Technical description: High primary circuit pressure (> 3 bar)
DIY fix possible
Check that the filling loop valves under the boiler are tightly closed.Bleed water from a radiator using a bleed key until the pressure gauge on the boiler falls back between 1 and 1.5 bar.Restart the boiler once the pressure is stabilised.
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Ariston models that show the 109 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ariston 109 fault code information on this page is sourced and cross-checked against the official Ariston service / installation manuals for each affected model.
- Ariston Alteas One manual (PDF)
- Ariston Clas ONE R manual (PDF)
- Ariston Clas ONE System manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026