BoilerFaultCodesZanussi SL Fault Code
The Zanussi SL fault code means: your boiler is currently running a service test at its lowest power setting and this is a status indicator rather than a functional error.. It appears on 2 Zanussi models in our database.
Technical description: End of fault history sequence display
What causes the Zanussi SL fault?
This indicator appears when a heating engineer has manually activated the 'service link' or minimum rate test mode during a routine inspection. It signifies that the boiler is being forced to run at its lowest possible power setting so the technician can accurately measure gas pressures and combustion levels. It is not a breakdown, but rather a sign that the boiler is in a specific diagnostic state.
DIY fix possible
Wait for the service or commissioning process to finishTurn the selector knob to the 'Reset' position and then back to 'On'Restart the boiler by switching the power off and on at the fused spur
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Zanussi models that show the SL fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Zanussi SL 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 31 August 2026