Keston Boilers Error Codes

E01

Boiler will not ignite, display shows E01 and burner does not light

Ignition Lockout

E02

Boiler locks out with E02, fan runs briefly then stops, no flame

Flame Detection Failure

E03

Boiler shows E03 and shuts down shortly after starting, primary flow temperature rises rapidly

Primary Overheat / High Limit Trip

E04

Boiler displays E04 and will not fire, fan may not start

Flue Fan / Air Pressure Fault

E05

Boiler shows E05, no heating or hot water, display may show low pressure symbol

Low Water Pressure / Water Pressure Switch Open

E06

Boiler locks out with E06, temperature readings appear incorrect or fluctuate rapidly

Flow Temperature Sensor Fault

E07

Boiler shows E07, may run briefly then shut down, return temperature reading abnormal

Return Temperature Sensor Fault

E08

Boiler displays E08 and will not start, fan may not run

Air Pressure Switch / Flue Differential Fault

E09

Boiler shows E09, no heating or hot water, pump may run briefly

Circulation Pump Fault

E10

Boiler displays E10, system pressure rises rapidly when heating, safety valve may discharge

Expansion Vessel / System Overpressure Fault

E11

Boiler shows E11, domestic hot water temperature unstable or excessively hot

DHW NTC Sensor Fault

E12

Boiler displays E12, no response to thermostat or programmer, boiler may stay off

External Control / Thermostat Circuit Fault

E13

Boiler shows E13, fan runs but ignition sequence does not start

Gas Valve Control Fault

E14

Boiler intermittently locks out with E14, especially in windy conditions

Flame Loss During Operation

E15

Boiler shows E15, no display backlight or intermittent power loss

Mains Supply / PCB Power Fault

E16

Boiler displays E16, condensate may be visible around base of boiler

Condensate Drain / Trap Fault

E17

Boiler shows E17, fan speed appears abnormal or noisy

Fan Speed / Tachometer Fault

E18

Boiler intermittently shows E18, particularly when switching between heating and hot water

Diverter Valve Position Fault

E19

Boiler shows E19, DHW flow is detected but burner does not fire

DHW Flow Detection Fault

E20

Boiler displays E20, burner shuts down shortly after lighting, primary temperature rises too quickly

Primary Flow Restriction / Heat Exchanger Blockage

E21

Boiler shows E21, display may indicate sensor mismatch or internal communication error

Internal Communication / PCB Sensor Bus Fault

E22

Boiler intermittently shows E22, particularly after power cuts or brownouts

Supply Voltage / Brownout Fault

E23

Boiler shows E23, safety thermostat has tripped and must be manually reset

Manual Reset Overheat Thermostat Trip

E24

Boiler displays E24, internal leak or low insulation resistance detected

Internal Water Leak / Earth Fault

E25

Boiler shows E25, CH flow temperature rises too quickly at low load

Low Flow / Minimum Flow Rate Fault

E26

Boiler intermittently shows E26, particularly when DHW demand is low

DHW Overheat / Flow Restriction

E27

Boiler shows E27, external sensor or weather compensation not detected or faulty

Outdoor Sensor / Weather Compensation Fault

Symptom

Boiler casing feels excessively hot or there is a smell of hot dust or plastic

Overheating Casing / Poor Ventilation

Symptom

Boiler fires but hot water temperature at taps is poor or fluctuates

Inadequate or Unstable Domestic Hot Water

Symptom

Boiler flue terminal shows white staining or water dripping excessively

Condensate / Flue Condensation Issue

Symptom

Boiler frequently loses pressure and needs topping up every few days

Chronic Pressure Loss

Symptom

Boiler is very noisy during operation, with whistling, droning, or vibration

Excessive Operational Noise

Symptom

Boiler leaking water from underneath the casing or from pipe connections

Internal Water Leak

Symptom

Boiler locks out more often in very cold weather, with visible condensate issues

Frozen or Restricted Condensate Discharge

Symptom

Boiler makes loud banging or kettling noises during operation

Kettling / Localised Boiling in Heat Exchanger

Symptom

Boiler runs but radiators do not get hot or only partially heat up

Poor Central Heating Circulation

Symptom

Boiler short cycles, frequently turning on and off with little heat delivered

Short Cycling / Oversized Boiler or Control Issue

Symptom

Boiler starts then shuts down after a few seconds without showing a specific error code

Flame Establishment Instability

Symptom

Boiler will not start at all, no lights or display

No Power / Dead Boiler

Symptom

Radiators get hot when only hot water is demanded, or hot water is poor when heating is on

Diverter Valve Cross-Leak or Stuck Position

Symptom

Strong smell of gas near the boiler, whether running or off

Gas Leak at Boiler