BoilerFaultCodesZanussi F4 Fault Code
The Zanussi F4 fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely regulate heat.. It appears on 1 Zanussi model in our database.
Technical description: Flow Thermistor Fault
What causes the Zanussi F4 fault?
This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water being sent to your taps and radiators. The most common reason is that the sensor has physically failed or developed an electrical short, though loose or damaged internal wiring can also prevent the boiler from reading the temperature correctly.
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 F4 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Zanussi F4 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