L5 or F5 High

Zanussi L5 or F5 Fault Code

Also written as L5ORF5 — same fault.

The Zanussi L5 or F5 fault code means: your boiler has lost the ability to read the temperature of the water returning to it, so it has shut down as a precaution to prevent overheating.. It appears on 1 Zanussi model 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: RETURN THERMISTOR FAULT
Typical repair cost £120-200 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Zanussi models that show the L5 or F5 fault code

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

Source

Zanussi L5 or F5 fault code information on this page is sourced and cross-checked against the official Zanussi service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026