F42 High

Ferroli F42 Fault Code

The Ferroli F42 fault code means: your boiler is struggling to detect the flow of water because a sensor inside the unit is providing an incorrect reading, which prevents it from safely heating your home or water.. It appears on 7 Ferroli models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Flow sensor fault
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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Ferroli models that show the F42 fault code

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

Source

Ferroli F42 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