BoilerFaultCodesBiasi FL Fault Code
The Biasi FL fault code means: your boiler has detected that the water pressure in your heating system has dropped too low and needs to be topped up to function correctly.. It appears on 2 Biasi models in our database.
Technical description: Filling request: The boiler works regularly and the display shows all the icons, but the signal FL is flashing every 1 sec
DIY fix possible
Locate the external filling loop, which is usually a flexible silver hose connecting two pipes underneath the boiler.Slowly open the tap or valve on the filling loop to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the tap or valve tightly once the correct pressure is reached to stop the flow.
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Biasi models that show the FL fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Biasi FL fault code information on this page is sourced and cross-checked against the official Biasi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026