d4 Low

Ferroli d4 Fault Code

Also written as D4 — same fault.

The Ferroli d4 fault code means: your boiler is currently taking a temporary break to protect its internal components from overheating, which is a normal safety feature after the system has reached its operating limit.. It appears on 3 Ferroli models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Safety pause time

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 d4 fault code

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

Source

Ferroli d4 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 7 July 2026