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.
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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…
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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 1 flash + LED 1Keston · Celsius 25 and 25P boilers · United KingdomLockout 1 flash + LED 1 — Flow overheat safety lockoutOne red lockout flash with diagnostic LED 1 illuminated identifies operation of the flow overheat thermostat.Lockout 1 flash + LED 2Keston · Celsius 25 and 25P boilers · United KingdomLockout 1 flash + LED 2 — Cabinet overheat safety lockoutOne red lockout flash with diagnostic LED 2 illuminated identifies a cabinet overheat condition or operated cabinet thermal…Lockout 1 flash + LED 3Keston · Celsius 25 and 25P boilers · United KingdomLockout 1 flash + LED 3 — Flue overheat safety lockoutOne red lockout flash with diagnostic LED 3 illuminated identifies operation of the flue overheat thermostat.Lockout 1 flash + LED 4Keston · Celsius 25 and 25P boilers · United KingdomLockout 1 flash + LED 4 — Spare sensor circuit or wiring-loom faultOne red lockout flash with diagnostic LED 4 illuminated indicates an unexpected fault on the spare sensor connection…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…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 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 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 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 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 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.Mains LED rapid flashKeston · Celsius 25 and 25P boilers · United KingdomMains LED rapid flash — No power available to the boiler controlsThe green mains indicator flashes rapidly when the boiler control system is not receiving the expected usable power…Mains LED slow flashKeston · Celsius 25 and 25P boilers · United KingdomMains LED slow flash — External controls are not calling for heatA slowly flashing green mains indicator means the boiler is powered but the external controls are not requesting…RED-LOCKOUTKeston · Keston 130 condensing gas boiler · United Kingdom and IrelandRed lockout light – Keston 130 boiler fault indicationKeston documents that the 130 has entered lockout when the red lamp alone remains illuminated. The boiler has…RED-LOCKOUTKeston · Keston 170 condensing gas boiler · United Kingdom and IrelandRed lockout light – Keston 170 boiler fault indicationKeston documents that the 170 has entered lockout when the red lamp alone remains illuminated. The boiler has…RED-LOCKOUTKeston · Keston 260 commercial condensing boiler · United Kingdom and IrelandRed lockout light – Keston 260 boiler fault indicationKeston documents a red lockout lamp for each module of the 260. If the red lamp alone remains…RED-LOCKOUTKeston · Keston 340 commercial condensing boiler · United Kingdom and IrelandRed lockout light – Keston 340 boiler fault indicationKeston documents a red lockout lamp for each module of the 340. If the red lamp alone remains…E01Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE01 – Ignition failure after five attemptsKeston documents E01 for the C36 and C36P Combi as “Ignition failure after five attempts”. Match this code…E02Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE02 – False flame detected before ignitionKeston documents E02 for the C36 and C36P Combi as “False flame detected before ignition”. Match this code…E03Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE03 – Boiler overheatKeston documents E03 for the C36 and C36P Combi as “Boiler overheat”. Match this code to the exact…E05Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE05 – Fan failureKeston documents E05 for the C36 and C36P Combi as “Fan failure”. Match this code to the exact…E07Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE07 – Flue overheatKeston documents E07 for the C36 and C36P Combi as “Flue overheat”. Match this code to the exact…E08Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE08 – Flame-circuit errorKeston documents E08 for the C36 and C36P Combi as “Flame-circuit error”. Match this code to the exact…E09Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE09 – Valve-drive errorKeston documents E09 for the C36 and C36P Combi as “Valve-drive error”. Match this code to the exact…E10Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE10 – Control-box errorKeston documents E10 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E11Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE11 – Flow/return sensor calibration test failedKeston documents E11 for the C36 and C36P Combi as “Flow/return sensor calibration test failed”. Match this code…E12Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE12 – Control-box errorKeston documents E12 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E13Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE13 – Control-box errorKeston documents E13 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E14Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE14 – Control-box errorKeston documents E14 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E15Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE15 – Control-box errorKeston documents E15 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E16Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE16 – Control-box errorKeston documents E16 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E17Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE17 – Control-box errorKeston documents E17 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E18Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE18 – Control-box errorKeston documents E18 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E19Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE19 – Control-box errorKeston documents E19 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E20Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE20 – Control-box errorKeston documents E20 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E21Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE21 – Control-box errorKeston documents E21 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E22Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE22 – Control-box errorKeston documents E22 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E23Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE23 – Water filling errorKeston documents E23 for the C36 and C36P Combi as “Water filling error”. Match this code to the…E24Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE24 – Water pressure lost four times in 24 hoursKeston documents E24 for the C36 and C36P Combi as “Water pressure lost four times in 24 hours”.…E25Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE25 – Control-box errorKeston documents E25 for the C36 and C36P Combi as “Control-box error”. Match this code to the exact…E26Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE26 – Flame signal lost five times in four minutesKeston documents E26 for the C36 and C36P Combi as “Flame signal lost five times in four minutes”.…E30Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE30 – Flow sensor short circuitKeston documents E30 for the C36 and C36P Combi as “Flow sensor short circuit”. Match this code to…E31Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE31 – Flow sensor open circuitKeston documents E31 for the C36 and C36P Combi as “Flow sensor open circuit”. Match this code to…E32Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE32 – DHW sensor short circuitKeston documents E32 for the C36 and C36P Combi as “DHW sensor short circuit”. Match this code to…E33Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE33 – DHW sensor open circuitKeston documents E33 for the C36 and C36P Combi as “DHW sensor open circuit”. Match this code to…E34Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE34 – Mains-supply voltage below 180 VKeston documents E34 for the C36 and C36P Combi as “Mains-supply voltage below 180 V”. Match this code…E35Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE35 – Incorrect mains-supply frequencyKeston documents E35 for the C36 and C36P Combi as “Incorrect mains-supply frequency”. Match this code to the…E37Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE37 – Water pressure errorKeston documents E37 for the C36 and C36P Combi as “Water pressure error”. Match this code to the…E38Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE38 – Reset key faultKeston documents E38 for the C36 and C36P Combi as “Reset key fault”. Match this code to the…E40Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE40 – Water pressure too highKeston documents E40 for the C36 and C36P Combi as “Water pressure too high”. Match this code to…E41Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE41 – Fascia-to-control-box communication errorKeston documents E41 for the C36 and C36P Combi as “Fascia-to-control-box communication error”. Match this code to the…E43Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE43 – Return sensor short circuitKeston documents E43 for the C36 and C36P Combi as “Return sensor short circuit”. Match this code to…E44Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE44 – Return sensor open circuitKeston documents E44 for the C36 and C36P Combi as “Return sensor open circuit”. Match this code to…E45Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE45 – Flue sensor short circuitKeston documents E45 for the C36 and C36P Combi as “Flue sensor short circuit”. Match this code to…E46Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE46 – Flue sensor open circuitKeston documents E46 for the C36 and C36P Combi as “Flue sensor open circuit”. Match this code to…E99Keston · Keston C36 and C36P Combi boilers · United Kingdom and IrelandE99 – Fascia-to-control-box communication error (same as E41)Keston documents E99 for the C36 and C36P Combi as “Fascia-to-control-box communication error (same as E41)”. Match this…B18Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB18 – Flow temperature exceeds 95°CKeston documents B18 for the C45, C40P, C55 and C55P as “Flow temperature exceeds 95°C”. This meaning applies…B19Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB19 – Return temperature exceeds 95°CKeston documents B19 for the C45, C40P, C55 and C55P as “Return temperature exceeds 95°C”. This meaning applies…B24Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB24 – Return temperature exceeds flow temperatureKeston documents B24 for the C45, C40P, C55 and C55P as “Return temperature exceeds flow temperature”. This meaning…B25Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB25 – Flow temperature climbing too quicklyKeston documents B25 for the C45, C40P, C55 and C55P as “Flow temperature climbing too quickly”. This meaning…B26Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB26 – Low water pressureKeston documents B26 for the C45, C40P, C55 and C55P as “Low water pressure”. This meaning applies to…B28Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB28 – No fan signalKeston documents B28 for the C45, C40P, C55 and C55P as “No fan signal”. This meaning applies to…B29Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB29 – Incorrect fan signalKeston documents B29 for the C45, C40P, C55 and C55P as “Incorrect fan signal”. This meaning applies to…B30Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB30 – Flow and return temperature difference too highKeston documents B30 for the C45, C40P, C55 and C55P as “Flow and return temperature difference too high”.…B65Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandB65 – Waiting for fan to startKeston documents B65 for the C45, C40P, C55 and C55P as “Waiting for fan to start”. This meaning…E00Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE00 – Flame detected when not expectedKeston documents E00 for the C45, C40P, C55 and C55P as “Flame detected when not expected”. This meaning…E02Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE02 – No ignition after restartKeston documents E02 for the C45, C40P, C55 and C55P as “No ignition after restart”. This meaning applies…E03Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE03 – Gas valve faulty or disconnectedKeston documents E03 for the C45, C40P, C55 and C55P as “Gas valve faulty or disconnected”. This meaning…E04Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE04 – Power reset while boiler was in lockoutKeston documents E04 for the C45, C40P, C55 and C55P as “Power reset while boiler was in lockout”.…E11Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE11 – Internal electronics errorKeston documents E11 for the C45, C40P, C55 and C55P as “Internal electronics error”. This meaning applies to…E12Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE12 – Thermal fuse blown or flue overheat thermostat activatedKeston documents E12 for the C45, C40P, C55 and C55P as “Thermal fuse blown or flue overheat thermostat…E18Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE18 – Flow overheatKeston documents E18 for the C45, C40P, C55 and C55P as “Flow overheat”. This meaning applies to this…E19Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE19 – Maximum return temperature exceededKeston documents E19 for the C45, C40P, C55 and C55P as “Maximum return temperature exceeded”. This meaning applies…E25Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE25 – Flow temperature increased too quicklyKeston documents E25 for the C45, C40P, C55 and C55P as “Flow temperature increased too quickly”. This meaning…E28Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE28 – Fan not rotatingKeston documents E28 for the C45, C40P, C55 and C55P as “Fan not rotating”. This meaning applies to…E30Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE30 – Flow and return temperature difference too highKeston documents E30 for the C45, C40P, C55 and C55P as “Flow and return temperature difference too high”.…E31Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE31 – Flow thermistor short circuitKeston documents E31 for the C45, C40P, C55 and C55P as “Flow thermistor short circuit”. This meaning applies…E32Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE32 – Return thermistor short circuitKeston documents E32 for the C45, C40P, C55 and C55P as “Return thermistor short circuit”. This meaning applies…E36Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE36 – Flow thermistor open circuitKeston documents E36 for the C45, C40P, C55 and C55P as “Flow thermistor open circuit”. This meaning applies…E37Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE37 – Return thermistor open circuitKeston documents E37 for the C45, C40P, C55 and C55P as “Return thermistor open circuit”. This meaning applies…E44Keston · Keston C45, C40P, C55 and C55P condensing boilers · United Kingdom and IrelandE44 – Low water pressureKeston documents E44 for the C45, C40P, C55 and C55P as “Low water pressure”. This meaning applies to…b18Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb18 – Keston C90/C110 error codeKeston documents b18 for C90 and C110 boiler modules as “Module flow temperature exceeded 95°C”. The manual classifies…b19Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb19 – Keston C90/C110 error codeKeston documents b19 for C90 and C110 boiler modules as “Module return temperature exceeded 95°C”. The manual classifies…b24Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb24 – Keston C90/C110 error codeKeston documents b24 for C90 and C110 boiler modules as “Module water circulation is reversed”. The manual classifies…b25Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb25 – Keston C90/C110 error codeKeston documents b25 for C90 and C110 boiler modules as “Module temperature is rising too quickly”. The manual…b26Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb26 – Keston C90/C110 error codeKeston documents b26 for C90 and C110 boiler modules as “Low water pressure”. The manual classifies it as…b28Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb28 – Keston C90/C110 error codeKeston documents b28 for C90 and C110 boiler modules as “No fan signal; the fan motor may be…b29Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb29 – Keston C90/C110 error codeKeston documents b29 for C90 and C110 boiler modules as “Fan running when it is not required”. The…b30Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb30 – Keston C90/C110 error codeKeston documents b30 for C90 and C110 boiler modules as “Water circulation is too slow”. The manual classifies…b65Keston · Keston C90 and C110 condensing boilers · United Kingdom and Irelandb65 – Keston C90/C110 error codeKeston documents b65 for C90 and C110 boiler modules as “Waiting for the fan to start; the fan…E00Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE00 – Keston C90/C110 error codeKeston documents E00 for C90 and C110 boiler modules as “Flame detected when not expected”. The manual classifies…E02Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE02 – Keston C90/C110 error codeKeston documents E02 for C90 and C110 boiler modules as “No ignition after restart”. The manual classifies it…E03Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE03 – Keston C90/C110 error codeKeston documents E03 for C90 and C110 boiler modules as “Gas valve faulty or not connected”. The manual…E04Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE04 – Keston C90/C110 error codeKeston documents E04 for C90 and C110 boiler modules as “Power reset while the module was in lockout”.…E11Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE11 – Keston C90/C110 error codeKeston documents E11 for C90 and C110 boiler modules as “Internal electronics error”. The manual classifies it as…E12Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE12 – Keston C90/C110 error codeKeston documents E12 for C90 and C110 boiler modules as “Thermal fuse blown or flue-overheat thermostat activated”. The…E18Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE18 – Keston C90/C110 error codeKeston documents E18 for C90 and C110 boiler modules as “Flow overheat”. The manual classifies it as a…E19Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE19 – Keston C90/C110 error codeKeston documents E19 for C90 and C110 boiler modules as “Maximum return temperature exceeded”. The manual classifies it…E25Keston · Keston C90 and C110 condensing boilers · United Kingdom and IrelandE25 – Keston C90/C110 error codeKeston documents E25 for C90 and C110 boiler modules as “Flow temperature increased too quickly”. The manual classifies…