BoilerFaultCodesZanussi L1 Fault Code
The Zanussi L1 fault code means: your boiler has shut down because the water inside it has become too hot, usually due to a lack of circulation or a blockage in the system.. It appears on 3 Zanussi models in our database.
Technical description: Flow Temp Overheat Lockout
What causes the Zanussi L1 fault?
This fault occurs when the internal sensors detect that the water is heating up too quickly or has reached a dangerously high temperature. The most common reason is that the water cannot move through the boiler properly, which is often caused by a failed pump, a blockage of sludge in the system, or air trapped within the unit.
This issue is more frequent during the first cold spell of autumn, when the heating is turned on after a long period of inactivity and the pump has seized up.
DIY fix possible
Check that your radiator valves are fully open.Ensure the boiler pressure is between 1 and 1.5 bar on the gauge.Reset the boiler by turning the control knob to 'Reset' and then back to 'On'.
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Zanussi models that show the L1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Zanussi L1 fault code information on this page is sourced and cross-checked against the official Zanussi service / installation manuals for each affected model.
- Zanussi Ultra Combi manual (PDF)
- Zanussi Ultra Plus Combi manual (PDF)
- Zanussi Ultra System manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026