Defro
Defro Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
Advertisements
E01
Boiler does not ignite, burner does not start, display shows E01 shortly after call for heat or hot water.
Ignition Failure / No Flame Detection
E02
Boiler locks out with E02, fan starts but burner does not light, sometimes accompanied by multiple failed ignition attempts.
Gas Valve or Gas Supply Fault
E03
Boiler shows E03 and shuts down, fan may run briefly, no ignition sequence starts.
Flue Gas / Air Pressure Switch Fault
E04
Boiler displays E04 and stops, temperature on display rises rapidly before shutdown.
Primary Flow Overheat / Safety Thermostat Trip
E05
Boiler shows E05, no heating or hot water, temperature reading may be unrealistic (very high or very low).
Flow Temperature Sensor (NTC) Fault
E06
Boiler displays E06, domestic hot water (DHW) temperature unstable or not recognized.
DHW Temperature Sensor (NTC) Fault
E07
Boiler shows E07, fan does not start or stops unexpectedly during operation.
Fan Motor / Fan Speed Feedback Fault
E08
Boiler displays E08, no heating or hot water, pump may run briefly then stop.
Circulation Pump Fault
E09
Boiler shows E09, no response to thermostat or control signals, sometimes intermittent.
Communication Fault Between User Interface and Main PCB
E10
Boiler displays E10, pressure gauge shows low or zero, boiler will not start.
Low Water Pressure / Pressure Switch Open
E11
Boiler shows E11, pressure gauge indicates high pressure (often above 3 bar), safety valve may discharge water.
High System Pressure / Expansion Fault
E12
Boiler displays E12, burner shuts down shortly after ignition, sometimes with noisy combustion.
Flame Instability / Poor Combustion
E13
Boiler shows E13, no hot water or heating, fan may run continuously.
Flue Gas Temperature Sensor Fault
E14
Boiler displays E14, DHW demand not recognized or boiler runs for heating when only hot water is requested.
DHW Flow Sensor / Turbine Fault
E15
Boiler shows E15, internal leak tray may contain water, boiler locks out.
Internal Water Leak / Leak Sensor Activated
E16
Boiler displays E16, outdoor temperature not recognized, weather compensation not working.
Outdoor Temperature Sensor Fault
E17
Boiler shows E17, no response to room thermostat or OpenTherm controller, heating does not start.
Room Thermostat / Control Signal Fault
E18
Boiler displays E18, internal temperature rises abnormally, fan speed may be high.
Internal Control Board Overheat
E19
Boiler shows E19, ignition occurs but flame is lost after a few seconds, repeated lockouts.
Flame Detection / Ionization Fault
E20
Boiler displays E20, no heating, pump may run but burner does not start, often after power disturbances.
Internal Control Board Error / EEPROM Fault
Symptom
Boiler display is on but completely unresponsive to button presses or knob adjustments.
User Interface Panel Failure
Symptom
Boiler display shows normal operation but there is no hot water at taps; heating works fine.
No DHW Production on Combi Boiler
Symptom
Boiler does not start at all, display is blank, no lights or response.
No Power / Electrical Supply Fault
Symptom
Boiler emits a burning smell or plastic odor during operation.
Overheating Component / Electrical Insulation Smell
Symptom
Boiler fan runs continuously even when there is no heating or hot water demand.
Fan Overrun / Stuck Relay
Symptom
Boiler flue terminal drips water or white staining appears on the wall below the terminal.
Condensate Management / Flue Condensation Issue
Symptom
Boiler frequently locks out during very cold weather, condensate pipe outside is icy.
Frozen Condensate Drain
Symptom
Boiler frequently loses pressure over days or weeks, requiring regular topping up.
Chronic Pressure Loss / Micro-Leak
Symptom
Boiler ignites with a loud bang or pop, especially after a long off period.
Delayed Ignition
Symptom
Boiler leaking water from underneath, small puddle forming below the Defro unit.
General Internal Leak / Hydraulic Seal Failure
Symptom
Boiler makes loud banging or knocking noises when starting or stopping, sometimes called kettling.
Heat Exchanger Kettling / Localized Boiling
Symptom
Boiler runs but produces only lukewarm domestic hot water, even at maximum setting.
Insufficient DHW Output
Symptom
Boiler runs but radiators do not get hot or only partially warm up.
Poor Heating Circulation / Balancing Issue
Symptom
Boiler starts and stops frequently in short cycles, even when heating demand is constant.
Short Cycling / Oversizing or Control Issue
Symptom
Boiler vibrates excessively and transmits noise to the wall or pipework during operation.
Mechanical Vibration / Mounting Fault
Symptom
Domestic hot water temperature fluctuates between hot and cold while a tap is running.
DHW Temperature Instability
Symptom
Radiators get hot even when there is no call for heating, especially when hot water is used.
Unwanted Heating / Diverter Valve Bypass
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E01 |
Boiler does not ignite, burner does not start, display shows E01 shortly after call for heat or hot water.
|
Ignition Failure / No Flame Detection | View Details |
| E02 |
Boiler locks out with E02, fan starts but burner does not light, sometimes accompanied by multiple failed ignition attempts.
|
Gas Valve or Gas Supply Fault | View Details |
| E03 |
Boiler shows E03 and shuts down, fan may run briefly, no ignition sequence starts.
|
Flue Gas / Air Pressure Switch Fault | View Details |
| E04 |
Boiler displays E04 and stops, temperature on display rises rapidly before shutdown.
|
Primary Flow Overheat / Safety Thermostat Trip | View Details |
| E05 |
Boiler shows E05, no heating or hot water, temperature reading may be unrealistic (very high or very low).
|
Flow Temperature Sensor (NTC) Fault | View Details |
| E06 |
Boiler displays E06, domestic hot water (DHW) temperature unstable or not recognized.
|
DHW Temperature Sensor (NTC) Fault | View Details |
| E07 |
Boiler shows E07, fan does not start or stops unexpectedly during operation.
|
Fan Motor / Fan Speed Feedback Fault | View Details |
| E08 |
Boiler displays E08, no heating or hot water, pump may run briefly then stop.
|
Circulation Pump Fault | View Details |
| E09 |
Boiler shows E09, no response to thermostat or control signals, sometimes intermittent.
|
Communication Fault Between User Interface and Main PCB | View Details |
| E10 |
Boiler displays E10, pressure gauge shows low or zero, boiler will not start.
|
Low Water Pressure / Pressure Switch Open | View Details |
| E11 |
Boiler shows E11, pressure gauge indicates high pressure (often above 3 bar), safety valve may discharge water.
|
High System Pressure / Expansion Fault | View Details |
| E12 |
Boiler displays E12, burner shuts down shortly after ignition, sometimes with noisy combustion.
|
Flame Instability / Poor Combustion | View Details |
| E13 |
Boiler shows E13, no hot water or heating, fan may run continuously.
|
Flue Gas Temperature Sensor Fault | View Details |
| E14 |
Boiler displays E14, DHW demand not recognized or boiler runs for heating when only hot water is requested.
|
DHW Flow Sensor / Turbine Fault | View Details |
| E15 |
Boiler shows E15, internal leak tray may contain water, boiler locks out.
|
Internal Water Leak / Leak Sensor Activated | View Details |
| E16 |
Boiler displays E16, outdoor temperature not recognized, weather compensation not working.
|
Outdoor Temperature Sensor Fault | View Details |
| E17 |
Boiler shows E17, no response to room thermostat or OpenTherm controller, heating does not start.
|
Room Thermostat / Control Signal Fault | View Details |
| E18 |
Boiler displays E18, internal temperature rises abnormally, fan speed may be high.
|
Internal Control Board Overheat | View Details |
| E19 |
Boiler shows E19, ignition occurs but flame is lost after a few seconds, repeated lockouts.
|
Flame Detection / Ionization Fault | View Details |
| E20 |
Boiler displays E20, no heating, pump may run but burner does not start, often after power disturbances.
|
Internal Control Board Error / EEPROM Fault | View Details |
| – |
Boiler display is on but completely unresponsive to button presses or knob adjustments.
|
User Interface Panel Failure | View Details |
| – |
Boiler display shows normal operation but there is no hot water at taps; heating works fine.
|
No DHW Production on Combi Boiler | View Details |
| – |
Boiler does not start at all, display is blank, no lights or response.
|
No Power / Electrical Supply Fault | View Details |
| – |
Boiler emits a burning smell or plastic odor during operation.
|
Overheating Component / Electrical Insulation Smell | View Details |
| – |
Boiler fan runs continuously even when there is no heating or hot water demand.
|
Fan Overrun / Stuck Relay | View Details |
| – |
Boiler flue terminal drips water or white staining appears on the wall below the terminal.
|
Condensate Management / Flue Condensation Issue | View Details |
| – |
Boiler frequently locks out during very cold weather, condensate pipe outside is icy.
|
Frozen Condensate Drain | View Details |
| – |
Boiler frequently loses pressure over days or weeks, requiring regular topping up.
|
Chronic Pressure Loss / Micro-Leak | View Details |
| – |
Boiler ignites with a loud bang or pop, especially after a long off period.
|
Delayed Ignition | View Details |
| – |
Boiler leaking water from underneath, small puddle forming below the Defro unit.
|
General Internal Leak / Hydraulic Seal Failure | View Details |
| – |
Boiler makes loud banging or knocking noises when starting or stopping, sometimes called kettling.
|
Heat Exchanger Kettling / Localized Boiling | View Details |
| – |
Boiler runs but produces only lukewarm domestic hot water, even at maximum setting.
|
Insufficient DHW Output | View Details |
| – |
Boiler runs but radiators do not get hot or only partially warm up.
|
Poor Heating Circulation / Balancing Issue | View Details |
| – |
Boiler starts and stops frequently in short cycles, even when heating demand is constant.
|
Short Cycling / Oversizing or Control Issue | View Details |
| – |
Boiler vibrates excessively and transmits noise to the wall or pipework during operation.
|
Mechanical Vibration / Mounting Fault | View Details |
| – |
Domestic hot water temperature fluctuates between hot and cold while a tap is running.
|
DHW Temperature Instability | View Details |
| – |
Radiators get hot even when there is no call for heating, especially when hot water is used.
|
Unwanted Heating / Diverter Valve Bypass | View Details |
No matching codes found
Advertisements