21 High

Ferroli 21 Fault Code

The Ferroli 21 fault code means: your boiler is currently unable to ignite, meaning it cannot produce heat or hot water because it is not receiving or burning gas safely.. It appears on 4 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: Boiler failed to light. Make sure that the gas isolation valve on the boiler and on the gas meter are open. Press the RESET button (2 Fig. 1).
Typical repair cost £120-250 (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 21 fault code

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

Source

Ferroli 21 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