BoilerFaultCodesWhat the manual says
Manufacturer manualMains (Green) ON, Boiler On (Yellow) OFF, Lockout (Red) Flashing twice every 2 seconds, DIAG LED 1 ON
From this model's manual
Verified against the Keston/Keston Celsius 25 installation & service manual.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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All 23 fault codes on the Celsius 25
Seeing a different code? Every code this model can display, in one place.
Boiler lost flame whilst runningBoiler off on frontCabinet overheatExternal controls not calling for heatF2Fan pcb faultyFan speed failureFlow OverheatFlow thermistor not connected or faultyFlue OverheatLockout lamp flashing 2 times every 2 secondsLockout lamp flashing 3 times every 2 secondsLockout lamp flashing 4 times every 2 secondsLockout lamp flashing 5 times every 2 secondsLockout lamp flashing 15 timesModulation LED 1 litModulation LED 2 litModulation LED 3 litNo power to boilerReturn thermistor not connected or faultySpare sensor/wiring loom faultWater pressure low