BoilerFaultCodesKeston L6 Fault Code
The Keston L6 fault code means: your boiler thinks it sees a flame even though it isn't currently trying to light, causing the system to shut down for safety.. It appears on 8 Keston models in our database.
Technical description: False flame lockout
What causes the Keston L6 fault?
This fault occurs when the boiler's control system detects an electrical signal suggesting a flame is present even though no gas is flowing. The most common reason is a contaminated or damaged flame sensing electrode sending a false signal, or moisture within the casing causing a short circuit. In some cases, the main circuit board may be failing and misinterpreting these electrical signals, leading to an immediate safety shutdown.
This issue can be more frequent during periods of high humidity or heavy rain, as internal dampness can interfere with the sensitive flame detection electronics.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Keston models that show the L6 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston L6 fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026