BoilerFaultCodesIdeal LF Fault Code
The Ideal LF fault code means: your boiler has tried to ignite three times but failed to stay alight, so it has shut down for safety.. It appears on 4 Ideal models in our database.
Technical description: If the boiler does not light after 3 attempts the fault codes L' 'F' will be displayed. Press the reset button (C); the boiler will then repeat its ignition sequence.
What causes the Ideal LF fault?
This fault occurs when the boiler's sensors cannot detect a flame after several attempts to start up. The most common reasons include a lack of gas reaching the unit, a build-up of carbon on the ignition parts, or a component failure that prevents the spark from catching. Essentially, the system shuts down because it cannot confirm it is safely burning fuel to create heat.
This fault is more common during the first cold snap of winter, as gas valves can occasionally stick after being idle over the summer or external gas regulators can be affected by extreme cold.
DIY fix possible
Check if your gas supply is active (e.g., check other gas appliances or your meter credit)Locate the reset button (marked 'C') and press it once to restart the ignition sequenceCheck if the condensate pipe (outside white plastic pipe) is frozen if the weather is very cold
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Gas Safe Register →Ideal models that show the LF fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal LF 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