How much does it cost to fix Ariston error code 109?

Typical repair cost for the Ariston 109 fault is £120-£350 including labour.

109 High

Ariston 109 Fault Code

Q: What does the Ariston 109 fault code mean?

Your boiler has detected that the water is circulating poorly or there is trapped air, causing it to shut down to prevent overheating.

The Ariston 109 fault code means: your boiler has detected that the water is circulating poorly or there is trapped air, causing it to shut down to prevent overheating.. It appears on 1 Ariston model in our database.

Technical description: Clas net one / Clas one CombiClas system one

Typical repair cost £120-£350 (including labour)

DIY fix possible

Check that the boiler pressure is between 1 and 1.5 bar on the gauge.Ensure all radiator valves are fully open.Bleed your radiators to remove any trapped air from the system.

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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.

Alteas One Repair: £120-£350

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026