BoilerFaultCodesZanussi F5 Fault Code
The Zanussi F5 fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water returning to the unit, causing it to stop working for safety.. It appears on 1 Zanussi model in our database.
Technical description: Return Thermistor Fault
What causes the Zanussi F5 fault?
This fault occurs when the boiler's control board receives an incorrect or missing signal from the sensor that monitors water temperature coming back from your radiators. The most common reason is that the sensor has physically failed due to age or internal wear, though it can also be caused by loose electrical connections or a fault on the main control 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 F5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Zanussi F5 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