121 High

Ferroli 121 Fault Code

The Ferroli 121 fault code means: your boiler has detected a temperature issue with the water flow, causing it to shut down for safety to prevent overheating.. It appears on 2 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 shut-down warning
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 121 fault code

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

Source

Ferroli 121 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