BoilerFaultCodesZanussi L5 Fault Code
The Zanussi L5 fault code means: your boiler has detected a problem with the sensor that monitors the temperature of the water coming back into the unit, causing it to shut down for safety.. It appears on 1 Zanussi model in our database.
Technical description: Return Thermistor Fault
What causes the Zanussi L5 fault?
This fault occurs when the boiler's control board receives an impossible or inconsistent reading from the sensor that monitors water returning from your radiators. The most common reason is that the sensor has physically failed or developed a short circuit, but it can also be triggered by damaged internal wiring or a fault with the main circuit board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Zanussi models that show the L5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Zanussi L5 fault code information on this page is sourced and cross-checked against the official Zanussi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026