BoilerFaultCodesFerroli A42 Fault Code
The Ferroli A42 fault code means: the boiler's internal thermometer is sending an incorrect signal to the control board, preventing the system from heating your water correctly.. It appears on 4 Ferroli models in our database.
Technical description: Flow sensor error – sensor damaged
What causes the Ferroli A42 fault?
This fault occurs when the boiler's control board loses communication with the temperature sensor or receives a reading that is outside of its normal operating range. The most common reason is that the internal thermistor has chemically degraded over time, but it can also be caused by loose or corroded electrical connections between the sensor and the main board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Ferroli models that show the A42 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ferroli A42 fault code information on this page is sourced and cross-checked against the official Ferroli service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026