How much does it cost to fix Ariston error code 40-50-80 (ll-ll-ll)?

Typical repair cost for the Ariston 40-50-80 (ll-ll-ll) fault is £120-200 including labour.

40-50-80 (ll-ll-ll) Medium

Ariston 40-50-80 (ll-ll-ll) Fault Code

Q: What does the Ariston 40-50-80 (ll-ll-ll) fault code mean?

Your boiler is struggling to detect the temperature of the water being used for your taps, which is preventing it from heating your water properly.

Also written as 405080LLLLLL — same fault.

The Ariston 40-50-80 (ll-ll-ll) fault code means: your boiler is struggling to detect the temperature of the water being used for your taps, which is preventing it from heating your water properly.. It appears on 4 Ariston models in our database.

Technical description: Thermistor «comfort» (open circuit)

Typical repair cost £120-200 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Ariston models that show the 40-50-80 (ll-ll-ll) fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Ariston 40-50-80 (ll-ll-ll) 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