Low
SL on Zanussi Ultra Plus Combi

Your boiler is currently running a service test at its lowest power setting and this is a status indicator rather than a functional error.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

End of fault history sequence display

From this model's manual
Verified against the Zanussi Ultra Plus Combi installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this 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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