Defro
Defro Furnaces Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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E01
The controller displays E01, and the furnace does not start the ignition sequence.
Ignition Failure – No Flame Detected at Start
E02
E02 displayed, and furnace shuts down shortly after ignition attempt.
Flame Loss During Operation
E03
E03 error, and the furnace stops; the display may indicate overheat or high boiler temperature.
Overheat Protection Activated
E04
E04 displayed; the furnace does not start the fan or ignition sequence.
Exhaust Fan / Draft Fan Failure
E05
E05 error, and the furnace stops; the controller may show a flue temperature fault.
Flue Gas Temperature Sensor Fault
E06
E06 displayed; the furnace does not respond to temperature changes or shows an unrealistic boiler temperature.
Boiler Temperature Sensor Error
E07
E07 error; the controller indicates a hopper or fuel temperature alarm.
Fuel Hopper Temperature Overlimit
E08
E08 displayed; the controller indicates a feeder or auger fault, and fuel is not being delivered.
Screw Feeder (Auger) Jam or Motor Fault
E09
E09 error; the controller indicates low water pressure or a lack of water in the system.
Low System Pressure / Water Shortage
E10
E10 displayed; the controller indicates a circulation pump fault or no flow.
Heating Circuit Pump Failure
E11
E11 error; the controller indicates a return temperature sensor fault.
Return Water Temperature Sensor Error
E12
E12 displayed; controller indicates room thermostat communication or sensor error.
Room Thermostat / Room Sensor Fault
E13
E13 error; controller indicates lambda sensor or O2 regulation fault (on Defro models with lambda control).
Lambda (Oxygen) Sensor Fault
E14
E14 displayed; controller indicates fan speed error or tachometer fault.
Combustion Fan Speed Feedback Error
E15
E15 error; controller indicates door or hatch open.
Door / Service Hatch Switch Open
E16
E16 displayed; controller indicates power supply or internal electronics error.
Control Board Power Supply Fault
E17
E17 error; controller indicates buffer tank sensor fault (for systems with buffer/accumulator tank).
Buffer Tank Temperature Sensor Error
E18
E18 displayed; controller indicates DHW (domestic hot water) sensor fault.
DHW Cylinder Temperature Sensor Error
E19
E19 error; controller indicates communication fault with expansion module or remote panel.
Communication Bus Error
E20
E20 displayed; controller indicates pellet/coal out or no flame due to lack of fuel.
Fuel Depletion / No Fuel Supply
Symptom
Ash pan fills very quickly and ash is unusually coarse or contains unburned fuel.
Inefficient Combustion / Incomplete Fuel Burn
Symptom
Boiler pressure rises excessively during heating and safety valve discharges water
Expansion Vessel / Safety Valve Issue
Symptom
Buttons on the Defro controller do not respond or respond intermittently
Keypad / Control Panel Fault
Symptom
Condensation or water dripping from the flue connection and back of the furnace.
Condensation in Flue / Low Return Temperature Corrosion Risk
Symptom
Controller display is blank or unreadable, but power is present at the unit
Display / User Interface Failure
Symptom
Frequent tripping of the main fuse or circuit breaker when furnace starts
Electrical Overload / Short Circuit
Symptom
Furnace casing or control panel becomes excessively hot to the touch during operation
Overheating of Casing / Insulation Degradation
Symptom
Furnace frequently shuts down and restarts, with large temperature swings.
Short Cycling / Poor Control Tuning
Symptom
Furnace makes loud banging or knocking noises in the pipes when heating.
Water Hammer / Boiling in Heat Exchanger
Symptom
Furnace runs but radiators remain lukewarm or cold, especially on upper floors.
Insufficient Heat Output / Poor Circulation
Symptom
Room thermostat calls for heat but the furnace does not start; the display shows standby with no error code.
Control Logic / External Control Inhibit
Symptom
Strong smoke or soot deposits visible at chimney outlet and on nearby surfaces.
Incomplete Combustion / Sooting
Symptom
Strong tar or creosote smell around the furnace and in the boiler room.
Low-Temperature Operation / Tar Formation
Symptom
Unusual grinding or squealing noise from the screw feeder area during operation.
Mechanical Wear or Obstruction in Screw Feeder
Symptom
Visible smoke leakage from furnace doors or joints into the boiler room.
Flue Gas Leakage / Poor Chimney Draft
Symptom
Water leaking from under the furnace or from boiler casing joints.
Boiler Water Leak
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E01 |
The controller displays E01, and the furnace does not start the ignition sequence.
|
Ignition Failure – No Flame Detected at Start | View Details |
| E02 |
E02 displayed, and furnace shuts down shortly after ignition attempt.
|
Flame Loss During Operation | View Details |
| E03 |
E03 error, and the furnace stops; the display may indicate overheat or high boiler temperature.
|
Overheat Protection Activated | View Details |
| E04 |
E04 displayed; the furnace does not start the fan or ignition sequence.
|
Exhaust Fan / Draft Fan Failure | View Details |
| E05 |
E05 error, and the furnace stops; the controller may show a flue temperature fault.
|
Flue Gas Temperature Sensor Fault | View Details |
| E06 |
E06 displayed; the furnace does not respond to temperature changes or shows an unrealistic boiler temperature.
|
Boiler Temperature Sensor Error | View Details |
| E07 |
E07 error; the controller indicates a hopper or fuel temperature alarm.
|
Fuel Hopper Temperature Overlimit | View Details |
| E08 |
E08 displayed; the controller indicates a feeder or auger fault, and fuel is not being delivered.
|
Screw Feeder (Auger) Jam or Motor Fault | View Details |
| E09 |
E09 error; the controller indicates low water pressure or a lack of water in the system.
|
Low System Pressure / Water Shortage | View Details |
| E10 |
E10 displayed; the controller indicates a circulation pump fault or no flow.
|
Heating Circuit Pump Failure | View Details |
| E11 |
E11 error; the controller indicates a return temperature sensor fault.
|
Return Water Temperature Sensor Error | View Details |
| E12 |
E12 displayed; controller indicates room thermostat communication or sensor error.
|
Room Thermostat / Room Sensor Fault | View Details |
| E13 |
E13 error; controller indicates lambda sensor or O2 regulation fault (on Defro models with lambda control).
|
Lambda (Oxygen) Sensor Fault | View Details |
| E14 |
E14 displayed; controller indicates fan speed error or tachometer fault.
|
Combustion Fan Speed Feedback Error | View Details |
| E15 |
E15 error; controller indicates door or hatch open.
|
Door / Service Hatch Switch Open | View Details |
| E16 |
E16 displayed; controller indicates power supply or internal electronics error.
|
Control Board Power Supply Fault | View Details |
| E17 |
E17 error; controller indicates buffer tank sensor fault (for systems with buffer/accumulator tank).
|
Buffer Tank Temperature Sensor Error | View Details |
| E18 |
E18 displayed; controller indicates DHW (domestic hot water) sensor fault.
|
DHW Cylinder Temperature Sensor Error | View Details |
| E19 |
E19 error; controller indicates communication fault with expansion module or remote panel.
|
Communication Bus Error | View Details |
| E20 |
E20 displayed; controller indicates pellet/coal out or no flame due to lack of fuel.
|
Fuel Depletion / No Fuel Supply | View Details |
| – |
Ash pan fills very quickly and ash is unusually coarse or contains unburned fuel.
|
Inefficient Combustion / Incomplete Fuel Burn | View Details |
| – |
Boiler pressure rises excessively during heating and safety valve discharges water
|
Expansion Vessel / Safety Valve Issue | View Details |
| – |
Buttons on the Defro controller do not respond or respond intermittently
|
Keypad / Control Panel Fault | View Details |
| – |
Condensation or water dripping from the flue connection and back of the furnace.
|
Condensation in Flue / Low Return Temperature Corrosion Risk | View Details |
| – |
Controller display is blank or unreadable, but power is present at the unit
|
Display / User Interface Failure | View Details |
| – |
Frequent tripping of the main fuse or circuit breaker when furnace starts
|
Electrical Overload / Short Circuit | View Details |
| – |
Furnace casing or control panel becomes excessively hot to the touch during operation
|
Overheating of Casing / Insulation Degradation | View Details |
| – |
Furnace frequently shuts down and restarts, with large temperature swings.
|
Short Cycling / Poor Control Tuning | View Details |
| – |
Furnace makes loud banging or knocking noises in the pipes when heating.
|
Water Hammer / Boiling in Heat Exchanger | View Details |
| – |
Furnace runs but radiators remain lukewarm or cold, especially on upper floors.
|
Insufficient Heat Output / Poor Circulation | View Details |
| – |
Room thermostat calls for heat but the furnace does not start; the display shows standby with no error code.
|
Control Logic / External Control Inhibit | View Details |
| – |
Strong smoke or soot deposits visible at chimney outlet and on nearby surfaces.
|
Incomplete Combustion / Sooting | View Details |
| – |
Strong tar or creosote smell around the furnace and in the boiler room.
|
Low-Temperature Operation / Tar Formation | View Details |
| – |
Unusual grinding or squealing noise from the screw feeder area during operation.
|
Mechanical Wear or Obstruction in Screw Feeder | View Details |
| – |
Visible smoke leakage from furnace doors or joints into the boiler room.
|
Flue Gas Leakage / Poor Chimney Draft | View Details |
| – |
Water leaking from under the furnace or from boiler casing joints.
|
Boiler Water Leak | View Details |
No matching codes found
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