BoilerFaultCodesJohnson Starley FL Fault Code
The Johnson Starley FL fault code means: your boiler has detected that the water pressure is too low for it to operate safely, which is why it has stopped working.. It appears on 1 Johnson Starley model in our database.
Technical description: Low pressure warning. Activates between 0.3bar & 0.8bar. The number which shows after FL is the pressure in bar (e.g. FL 03 = 0.3 bar of pressure).
DIY fix possible
Locate the external filling loop, which is usually a flexible silver hose with two small valves.Slowly open both valves to allow water into the system while watching the display.Close both valves tightly once the display shows the pressure is between 1.0 and 1.5 bar.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Johnson Starley models that show the FL fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Johnson Starley FL fault code information on this page is sourced and cross-checked against the official Johnson Starley service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026