Keston error codes
Find the meaning of Keston fault, warning and status codes, with model context, documented causes, safe checks and links to available manufacturer guidance.
444documented codes
20products and models
1product categories
About Keston error codes
An error code is a diagnostic clue, not a complete repair diagnosis. Keston may reuse similar-looking codes across different products, model generations or regions, so always confirm the complete code and exact model before following instructions or ordering parts.
This profile connects every indexed Keston code to its dedicated explanation page. Each page is structured around the search intent: a quick meaning, symptoms, likely causes, safe troubleshooting, reset guidance, applicable products and the point at which professional help is appropriate. Records marked as verified include the manufacturer or another authoritative technical source.
Start with the code shown on the display, then narrow the result by product or model. Do not assume that a reset has repaired the underlying fault. If a code returns, the product is unsafe, or diagnosis requires internal electrical, gas, refrigerant or moving components, stop and use an authorised technician.
Start here
Popular Keston codes
Lockout LED constant flashKeston · Celsius 25 and 25P boilers · United KingdomLockout LED constant flash — Fan PCB faultA constantly flashing red lockout indicator is identified by the manual as a fan-control PCB fault.Lockout 15 flashesKeston · Celsius 25 and 25P boilers · United KingdomLockout 15 flashes — Control PCB faultA repeating sequence of fifteen red lockout flashes followed by a pause indicates a control-board fault that does…Lockout 5 flashesKeston · Celsius 25 and 25P boilers · United KingdomLockout 5 flashes — Fan-speed failureFive red lockout flashes every two seconds indicate that fan speed has fallen below the required operating threshold.Lockout 4 flashesKeston · Celsius 25 and 25P boilers · United KingdomLockout 4 flashes — Low system-water pressureFour red lockout flashes every two seconds indicate that the boiler has detected insufficient system-water pressure.Lockout 3 flashes + LED 2Keston · Celsius 25 and 25P boilers · United KingdomLockout 3 flashes + LED 2 — Return thermistor disconnected or faultyThree red lockout flashes with diagnostic LED 2 illuminated identify a return-temperature thermistor circuit fault.Lockout 3 flashes + LED 1Keston · Celsius 25 and 25P boilers · United KingdomLockout 3 flashes + LED 1 — Flow thermistor disconnected or faultyThree red lockout flashes with diagnostic LED 1 illuminated identify a flow-temperature thermistor circuit fault.Lockout 2 flashes + LED 2Keston · Celsius 25 and 25P boilers · United KingdomLockout 2 flashes + LED 2 — Flame lost while runningTwo red lockout flashes with diagnostic LED 2 illuminated mean the boiler established a flame but lost it…Lockout 2 flashes + LED 1Keston · Celsius 25 and 25P boilers · United KingdomLockout 2 flashes + LED 1 — Ignition failureTwo red lockout flashes with diagnostic LED 1 illuminated mean the boiler has attempted to ignite repeatedly without…
Keston product groups
Code directory
Open advanced search →All Keston codes
Showing 401–444 of 444
LOW WATER PRESSUREKeston · Keston System² S30 gas boiler · United Kingdom and IrelandLOW WATER PRESSURE – Keston System² S30 error codeKeston documents “Low system water pressure” for the System² S30. This display message identifies a boiler-detected fault or…NO WATER FLOWKeston · Keston System² S30 gas boiler · United Kingdom and IrelandNO WATER FLOW – Keston System² S30 error codeKeston documents “No water flow” for the System² S30. This display message identifies a boiler-detected fault or safety…OUTSIDE SENSOR FAULTKeston · Keston System² S30 gas boiler · United Kingdom and IrelandOUTSIDE SENSOR FAULT – Keston System² S30 error codeKeston documents “Outside sensor fault” for the System² S30. This display message identifies a boiler-detected fault or safety…OVERHEAT LOCKOUTKeston · Keston System² S30 gas boiler · United Kingdom and IrelandOVERHEAT LOCKOUT – Keston System² S30 error codeKeston documents “Overheat lockout” for the System² S30. This display message identifies a boiler-detected fault or safety condition;…PCB FAULTKeston · Keston System² S30 gas boiler · United Kingdom and IrelandPCB FAULT – Keston System² S30 error codeKeston documents “Printed circuit board fault” for the System² S30. This display message identifies a boiler-detected fault or…PUMP DRY RUNKeston · Keston System² S30 gas boiler · United Kingdom and IrelandPUMP DRY RUN – Keston System² S30 error codeKeston documents “Pump dry-run protection” for the System² S30. This display message identifies a boiler-detected fault or safety…PUMP FAULTKeston · Keston System² S30 gas boiler · United Kingdom and IrelandPUMP FAULT – Keston System² S30 error codeKeston documents “Pump fault” for the System² S30. This display message identifies a boiler-detected fault or safety condition;…PUMP ROTOR BLOCKEDKeston · Keston System² S30 gas boiler · United Kingdom and IrelandPUMP ROTOR BLOCKED – Keston System² S30 error codeKeston documents “Pump rotor blocked” for the System² S30. This display message identifies a boiler-detected fault or safety…RETURN THERMISTOR FAULTKeston · Keston System² S30 gas boiler · United Kingdom and IrelandRETURN THERMISTOR FAULT – Keston System² S30 error codeKeston documents “Return thermistor fault” for the System² S30. This display message identifies a boiler-detected fault or safety…ROOM THERMOSTAT FAULTKeston · Keston System² S30 gas boiler · United Kingdom and IrelandROOM THERMOSTAT FAULT – Keston System² S30 error codeKeston documents “Room thermostat fault” for the System² S30. This display message identifies a boiler-detected fault or safety…SPARE PCB NOT SETKeston · Keston System² S30 gas boiler · United Kingdom and IrelandSPARE PCB NOT SET – Keston System² S30 error codeKeston documents “Replacement PCB not configured” for the System² S30. This display message identifies a boiler-detected fault or…TOO MANY RESTARTSKeston · Keston System² S30 gas boiler · United Kingdom and IrelandTOO MANY RESTARTS – Keston System² S30 error codeKeston documents “Too many restarts” for the System² S30. This display message identifies a boiler-detected fault or safety…AIR PRESSURE SWITCH NOT PROVINGKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomAIR PRESSURE SWITCH NOT PROVING – Keston 50/60/80 faultThe controller has not proved the required combustion airflow.AMBER POWER LIGHT OFFKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomAMBER POWER LIGHT OFF – Keston 50/60/80 faultThe boiler is not receiving its expected switched electrical supply.BURNER FAILS TO IGNITEKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomBURNER FAILS TO IGNITE – Keston 50/60/80 faultSpark and gas may be present but a stable burner flame is not established.FAN NOT RUNNINGKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomFAN NOT RUNNING – Keston 50/60/80 faultThe ignition sequence cannot continue because the combustion blower is not operating.FLAME NOT DETECTEDKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomFLAME NOT DETECTED – Keston 50/60/80 faultThe control does not receive a valid flame signal and proceeds to lockout.FLOW OVERHEAT THERMOSTAT OPENKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomFLOW OVERHEAT THERMOSTAT OPEN – Keston 50/60/80 faultA flow-temperature safety thermostat has interrupted the boiler supply.FLUE OVERHEAT THERMOSTAT OPENKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomFLUE OVERHEAT THERMOSTAT OPEN – Keston 50/60/80 faultThe flue-temperature safety circuit has interrupted boiler operation.GAS LOW PRESSURE SWITCH OPENKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomGAS LOW PRESSURE SWITCH OPEN – Keston 50/60/80 faultThe boiler safety circuit has not proved the required gas-supply pressure.GAS VALVE NOT ENERGISEDKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomGAS VALVE NOT ENERGISED – Keston 50/60/80 faultThe ignition sequence has reached the gas-control stage without the expected valve supply.IGNITION SEQUENCE NOT STARTINGKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomIGNITION SEQUENCE NOT STARTING – Keston 50/60/80 faultThe control sequence has stopped before the spark and gas-valve stage.LOW WATER PRESSURE SWITCH OPENKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomLOW WATER PRESSURE SWITCH OPEN – Keston 50/60/80 faultSystem pressure is insufficient for the boiler safety circuit to remain closed.NO IGNITION SPARKKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomNO IGNITION SPARK – Keston 50/60/80 faultThe burner cannot light because the expected high-voltage ignition spark is absent.RED LOCKOUT LIGHT ONLYKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomRED LOCKOUT LIGHT ONLY – Keston 50/60/80 faultThe boiler has failed to light or a safety device has interrupted operation.THERMAL FUSE OPENKeston · Legacy Keston 50, 60 and 80 condensing boilers · United KingdomTHERMAL FUSE OPEN – Keston 50/60/80 faultA non-resettable thermal protection device has interrupted the control circuit.BCC FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaBCC FAULT – legacy Keston Heat 45/55 error codeKeston documents “Boiler coding component fault” for the legacy Heat 45, 55, 45P and 55P controller. This is…CYLINDER THERMISTOR FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaCYLINDER THERMISTOR FAULT – legacy Keston Heat 45/55 error codeKeston documents “Cylinder thermistor fault” for the legacy Heat 45, 55, 45P and 55P controller. This is a…ERROR 20Keston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaERROR 20 – legacy Keston Heat 45/55 error codeKeston documents “False-flame lockout” for the legacy Heat 45, 55, 45P and 55P controller. This is a distinct…EXTERNAL INTERLOCK OFFKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaEXTERNAL INTERLOCK OFF – legacy Keston Heat 45/55 error codeKeston documents “External safety interlock operated” for the legacy Heat 45, 55, 45P and 55P controller. This is…FAN FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaFAN FAULT – legacy Keston Heat 45/55 error codeKeston documents “Fan fault” for the legacy Heat 45, 55, 45P and 55P controller. This is a distinct…FLAME LOSSKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaFLAME LOSS – legacy Keston Heat 45/55 error codeKeston documents “Flame loss during operation” for the legacy Heat 45, 55, 45P and 55P controller. This is…FLOW FLUE THERMISTOR FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaFLOW FLUE THERMISTOR FAULT – legacy Keston Heat 45/55 error codeKeston documents “Flow or flue thermistor fault” for the legacy Heat 45, 55, 45P and 55P controller. This…FLOW RETURN REVERSEDKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaFLOW RETURN REVERSED – legacy Keston Heat 45/55 error codeKeston documents “Flow and return connections reversed” for the legacy Heat 45, 55, 45P and 55P controller. This…FLOW THERMISTOR FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaFLOW THERMISTOR FAULT – legacy Keston Heat 45/55 error codeKeston documents “Flow thermistor fault” for the legacy Heat 45, 55, 45P and 55P controller. This is a…FLUE THERMISTOR FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaFLUE THERMISTOR FAULT – legacy Keston Heat 45/55 error codeKeston documents “Flue thermistor fault” for the legacy Heat 45, 55, 45P and 55P controller. This is a…IGNITION LOCKOUTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaIGNITION LOCKOUT – legacy Keston Heat 45/55 error codeKeston documents “Ignition lockout” for the legacy Heat 45, 55, 45P and 55P controller. This is a distinct…LOW MAINS VOLTAGEKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaLOW MAINS VOLTAGE – legacy Keston Heat 45/55 error codeKeston documents “Mains voltage below the permitted level” for the legacy Heat 45, 55, 45P and 55P controller.…LOW WATER PRESSUREKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaLOW WATER PRESSURE – legacy Keston Heat 45/55 error codeKeston documents “Low water pressure” for the legacy Heat 45, 55, 45P and 55P controller. This is a…OUTSIDE SENSOR FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaOUTSIDE SENSOR FAULT – legacy Keston Heat 45/55 error codeKeston documents “Outside sensor fault” for the legacy Heat 45, 55, 45P and 55P controller. This is a…OVERHEAT LOCKOUTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaOVERHEAT LOCKOUT – legacy Keston Heat 45/55 error codeKeston documents “Boiler overheat lockout” for the legacy Heat 45, 55, 45P and 55P controller. This is a…PCB FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaPCB FAULT – legacy Keston Heat 45/55 error codeKeston documents “Main controller fault” for the legacy Heat 45, 55, 45P and 55P controller. This is a…RETURN THERMISTOR FAULTKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaRETURN THERMISTOR FAULT – legacy Keston Heat 45/55 error codeKeston documents “Return thermistor fault” for the legacy Heat 45, 55, 45P and 55P controller. This is a…TOO MANY RESETSKeston · Legacy Keston Heat 45 and 55 commercial boilers · United Kingdom, Ireland and RomaniaTOO MANY RESETS – legacy Keston Heat 45/55 error codeKeston documents “Too many resets within 15 minutes” for the legacy Heat 45, 55, 45P and 55P controller.…