BoilerFaultCodesKeston L5 Fault Code
The Keston L5 fault code means: your boiler has been manually reset too many times in a short period and has locked itself out to prevent further damage or safety issues.. It appears on 8 Keston models in our database.
Technical description: 5 boiler resets in 15 minutes
What causes the Keston L5 fault?
This fault occurs when the boiler has been restarted five times within a fifteen-minute window, triggering a safety software block. It usually happens because an underlying issue prevented the burner from lighting, leading the user to repeatedly press reset until the system locked itself out out for protection. The root cause is typically a failure to detect a flame, often due to a worn ignition component or an inconsistent gas supply.
This fault is more frequent during very cold spells when frozen condensate pipes or freezing gas meters can cause the initial ignition failures that lead a homeowner to repeatedly reset the unit.
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 L5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Keston L5 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