BoilerFaultCodesFerroli F66 Fault Code
The Ferroli F66 fault code means: your boiler's main control board has detected an internal communication error, meaning it cannot process commands correctly.. It appears on 7 Ferroli models in our database.
Technical description: –
What causes the Ferroli F66 fault?
This fault occurs when the boiler's central brain, the main control board, experiences an internal electronics failure or loses the ability to talk to its sensors. The most common reason is a hardware malfunction within the PCB itself or a loose connection in the internal wiring harness that prevents data from flowing correctly.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Ferroli models that show the F66 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ferroli F66 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 27 April 2026