BoilerFaultCodesHeatline F6 Fault Code
The Heatline F6 fault code means: your boiler is having trouble communicating with the outside temperature sensor, which helps it run efficiently based on the weather.. It appears on 1 Heatline model in our database.
Technical description: External sensor fault (where fitted)
DIY fix possible
Locate the external sensor on an outside wall to check for obvious physical damage or loose wiresTurn the boiler power off and back on to see if the fault clearsIf the issue persists, the boiler will still provide heat but will revert to standard internal settings
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Heatline models that show the F6 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Heatline F6 fault code information on this page is sourced and cross-checked against the official Heatline service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026