fl- Low

Worcester Bosch fl- Fault Code

Also written as FL — same fault.

The Worcester Bosch fl- fault code means: your boiler is performing a routine initial startup procedure to fill its internal condensation trap and is not actually experiencing a fault.. It appears on 1 Worcester Bosch model in our database.

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.

Technical description: The boiler runs for 15 minutes at minimum heating output to fill the condensate trap, the display (K) alternates between 'fI-' and the flow temperature.

DIY fix possible

Wait 15 minutes for the automated cycle to completeEnsure the boiler power remains on during this periodObserve the display until the code disappears and the normal temperature is shown

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Worcester Bosch models that show the fl- fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch fl- fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026