A-4 Medium

Ferroli A-4 Fault Code

Also written as A4 — same fault.

The Ferroli A-4 fault code means: your boiler has stopped providing hot water because it is having trouble reading the temperature of the water used for your taps.. It appears on 2 Ferroli models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: D.H.W. sensor (42) not connected or D.H.W. temperature too high
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 A-4 fault code

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

Source

Ferroli A-4 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