BoilerFaultCodesIdeal L-F Fault Code
Also written as LF — same fault.
The Ideal L-F fault code means: your boiler has failed to light or maintain a flame, meaning your heating and hot water have stopped working.. It appears on 12 Ideal models in our database.
Technical description: Flame failure
What causes the Ideal L-F fault?
This fault occurs when the boiler's control system attempts to start the burner but cannot detect a stable flame. The most common reasons are a lack of gas supply to the unit, a worn-out ignition component that fails to create a spark, or a dirty internal sensor that cannot 'see' the flame once it has lit.
This fault is more common during the first cold snap of winter, as gas valves can occasionally stick after long periods of inactivity during the summer.
DIY fix possible
Check if other gas appliances, like a hob, are working to ensure gas is reaching your homeCheck if your gas meter has creditPress the 'Reset' button on the boiler control panel
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Ideal models that show the L-F fault code
Click a model for the full fault code list and model-specific repair notes.
- Classic FF 330 Repair: £120-250
- Icos HE Repair: £120-250
- Icos System Repair: £150-300
- Icos System Repair: £150-300
- Isar HE Repair: £150-300
- Isar HE Repair: £150-300
- Isar M30 / M100 Repair: £150-300
- Isar M30 / M100 Repair: £150-300
- Isar System Repair: £150-300
- Isar System Repair: £150-300
- Mexico HE Repair: £120-350
- Mexico Super 100FF / 125FF Repair: £150-300
Source
Ideal L-F fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026