How much does it cost to fix Ariston error code 40-50-70 (ll-ll-ll)?

Typical repair cost for the Ariston 40-50-70 (ll-ll-ll) fault is £120-220 including labour.

40-50-70 (ll-ll-ll) High

Ariston 40-50-70 (ll-ll-ll) Fault Code

Q: What does the Ariston 40-50-70 (ll-ll-ll) fault code mean?

Your boiler has detected a faulty sensor that monitors the temperature of the water used for your taps, causing it to stop producing hot water to prevent overheating.

Also written as 405070LLLLLL — same fault.

The Ariston 40-50-70 (ll-ll-ll) fault code means: your boiler has detected a faulty sensor that monitors the temperature of the water used for your taps, causing it to stop producing hot water to prevent overheating.. It appears on 4 Ariston models in our database.

Technical description: Thermistor «comfort» (short circuit)

Typical repair cost £120-220 (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 40-50-70 (ll-ll-ll) fault code

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

Source

Ariston 40-50-70 (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