Junkers
Junkers Water Heaters Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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A2
Water heater does not ignite; the display shows A2 shortly after a hot water tap is opened.
Ignition Failure – No Flame Detected
A3
The unit attempts to start but shuts down with A3; the fan may run briefly, and the burner does not stay lit.
Flue Gas Sensor / Exhaust Temperature Fault
A7
Display shows A7; water temperature reading is erratic or clearly wrong (e.g., shows 80°C when water is cold).
Domestic Hot Water Temperature Sensor Fault
A8
Heater locks out with A8; may occur after long operation at high temperature.
Primary Flow Temperature Sensor Fault / Overtemperature
A9
Display shows A9; water temperature fluctuates or unit cycles rapidly.
Return Temperature Sensor Fault / Sensor Mismatch
C1
Fan starts but unit locks out with C1; no ignition or very short ignition attempt.
Fan / Air Pressure Switch Fault
C6
Error C6 appears; fan may not start or runs at incorrect speed.
Fan Speed / Hall Sensor Fault
E1
E1 error; the heater does not start, or shuts down quickly after ignition.
Water Pressure / Flow Fault (for models with internal pump or pressure switch)
E2
E2 displayed; water temperature overshoots the setpoint then drops, with frequent cycling.
Outlet Temperature Control Fault
E3
E3 error; the unit may shut down during operation, especially in windy conditions.
Flue Gas / Draft Fault
E5
E5 displayed; the unit may not modulate correctly, causing very hot or very cool water.
Gas Modulation / Valve Control Error
E6
E6 error; ignition may be weak or absent, with no or few sparks heard.
Ignition Transformer / Ignition Control Fault
E8
E8 displayed; the unit may shut down during operation, often at high output.
Overtemperature at Heat Exchanger
E9
Display shows E9; unit may overheat and shut down, sometimes with noise from boiling water.
Overheat / Safety Temperature Limiter Tripped
EA
Unit locks out with EA; ignition sparks are heard but burner does not light or lights briefly then goes out.
Flame Detection Failure
F0
F0 appears intermittently; unit may continue to run but with unstable temperature.
General Sensor Fault / NTC Out of Range
F1
F1 displayed; heater does not start or stops shortly after starting.
Flow Sensor / Turbine Fault
F7
F7 appears; unit may lock out after ignition attempts, sometimes with delayed ignition or small bangs.
Flame Signal Error / Flame Present at Wrong Time
F9
F9 error; the heater may start but then shut down, especially at low flow rates.
Gas Valve Modulation / Combustion Control Fault
H11
H11 or a similar code; the unit may limit maximum temperature or power.
Service Interval Reached / Maintenance Code
H7
H7 displayed; the unit may still operate but with reduced performance or noisy combustion.
Maintenance Reminder / Combustion Quality Degradation
L0
Display shows L0 or a similar low-temperature/anti-freeze indication; the burner may fire briefly without hot water demand.
Frost Protection Operation
P1
P1 appears; the heater may not respond to hot water demand or shows incorrect flow.
Flow Sensor Calibration / Low Flow Detection Error
P2
P2 displayed; the unit may limit output temperature or shut down under high demand.
Maximum Temperature Limitation / Overload Protection
Symptom
Display is on but buttons or rotary knobs do not respond to input.
User Interface / Control Panel Failure
Symptom
Heater cycles on and off rapidly with very short burner runs, even at a single tap.
Short Cycling / Minimum Power Too High for Flow
Symptom
Heater does not start; display is blank and no lights are on.
No Power / Control Board Not Energized
Symptom
Hot water has a metallic or rusty color when first opened.
Corrosion / Rust Contamination
Symptom
Hot water has a strong rotten-egg (sulfur) smell.
Bacterial Contamination / Sulfide Reaction
Symptom
No hot water at any tap; the display is on, but the burner does not start and no error code is shown.
No Demand Detection / Flow Activation Failure
Symptom
The burner runs, but there is a strong smell of combustion or fumes near the heater.
Flue Gas Recirculation / Ventilation Problem
Symptom
The heater makes loud banging or knocking noises when starting or stopping.
Water Hammer / Delayed Ignition
Symptom
The pilot light will not stay lit on older Junkers pilot-type water heaters.
Pilot Flame Instability / Thermocouple Failure
Symptom
The water heater ignites, but hot water is only lukewarm even at the maximum temperature setting.
Insufficient Heating / Underfiring
Symptom
The water heater leaks from the flue condensate drain or around the flue connection.
Condensate / Flue Leak
Symptom
The water heater leaks water from the bottom of the casing.
Internal Water Leak
Symptom
Water heater emits a high-pitched whistling or humming noise during operation.
Acoustic Resonance / Flow Noise
Symptom
Water heater frequently shuts off due to overpressure, discharging water from the safety valve.
Overpressure / Expansion Control Problem
Symptom
Water heater starts but shuts off when another tap is opened or closed, causing temperature shocks.
Flow Interaction / Hydraulic Imbalance
Symptom
Water temperature fluctuates between hot and cold during a shower.
Temperature Instability / Cycling
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| A2 |
Water heater does not ignite; the display shows A2 shortly after a hot water tap is opened.
|
Ignition Failure – No Flame Detected | View Details |
| A3 |
The unit attempts to start but shuts down with A3; the fan may run briefly, and the burner does not stay lit.
|
Flue Gas Sensor / Exhaust Temperature Fault | View Details |
| A7 |
Display shows A7; water temperature reading is erratic or clearly wrong (e.g., shows 80°C when water is cold).
|
Domestic Hot Water Temperature Sensor Fault | View Details |
| A8 |
Heater locks out with A8; may occur after long operation at high temperature.
|
Primary Flow Temperature Sensor Fault / Overtemperature | View Details |
| A9 |
Display shows A9; water temperature fluctuates or unit cycles rapidly.
|
Return Temperature Sensor Fault / Sensor Mismatch | View Details |
| C1 |
Fan starts but unit locks out with C1; no ignition or very short ignition attempt.
|
Fan / Air Pressure Switch Fault | View Details |
| C6 |
Error C6 appears; fan may not start or runs at incorrect speed.
|
Fan Speed / Hall Sensor Fault | View Details |
| E1 |
E1 error; the heater does not start, or shuts down quickly after ignition.
|
Water Pressure / Flow Fault (for models with internal pump or pressure switch) | View Details |
| E2 |
E2 displayed; water temperature overshoots the setpoint then drops, with frequent cycling.
|
Outlet Temperature Control Fault | View Details |
| E3 |
E3 error; the unit may shut down during operation, especially in windy conditions.
|
Flue Gas / Draft Fault | View Details |
| E5 |
E5 displayed; the unit may not modulate correctly, causing very hot or very cool water.
|
Gas Modulation / Valve Control Error | View Details |
| E6 |
E6 error; ignition may be weak or absent, with no or few sparks heard.
|
Ignition Transformer / Ignition Control Fault | View Details |
| E8 |
E8 displayed; the unit may shut down during operation, often at high output.
|
Overtemperature at Heat Exchanger | View Details |
| E9 |
Display shows E9; unit may overheat and shut down, sometimes with noise from boiling water.
|
Overheat / Safety Temperature Limiter Tripped | View Details |
| EA |
Unit locks out with EA; ignition sparks are heard but burner does not light or lights briefly then goes out.
|
Flame Detection Failure | View Details |
| F0 |
F0 appears intermittently; unit may continue to run but with unstable temperature.
|
General Sensor Fault / NTC Out of Range | View Details |
| F1 |
F1 displayed; heater does not start or stops shortly after starting.
|
Flow Sensor / Turbine Fault | View Details |
| F7 |
F7 appears; unit may lock out after ignition attempts, sometimes with delayed ignition or small bangs.
|
Flame Signal Error / Flame Present at Wrong Time | View Details |
| F9 |
F9 error; the heater may start but then shut down, especially at low flow rates.
|
Gas Valve Modulation / Combustion Control Fault | View Details |
| H11 |
H11 or a similar code; the unit may limit maximum temperature or power.
|
Service Interval Reached / Maintenance Code | View Details |
| H7 |
H7 displayed; the unit may still operate but with reduced performance or noisy combustion.
|
Maintenance Reminder / Combustion Quality Degradation | View Details |
| L0 |
Display shows L0 or a similar low-temperature/anti-freeze indication; the burner may fire briefly without hot water demand.
|
Frost Protection Operation | View Details |
| P1 |
P1 appears; the heater may not respond to hot water demand or shows incorrect flow.
|
Flow Sensor Calibration / Low Flow Detection Error | View Details |
| P2 |
P2 displayed; the unit may limit output temperature or shut down under high demand.
|
Maximum Temperature Limitation / Overload Protection | View Details |
| – |
Display is on but buttons or rotary knobs do not respond to input.
|
User Interface / Control Panel Failure | View Details |
| – |
Heater cycles on and off rapidly with very short burner runs, even at a single tap.
|
Short Cycling / Minimum Power Too High for Flow | View Details |
| – |
Heater does not start; display is blank and no lights are on.
|
No Power / Control Board Not Energized | View Details |
| – |
Hot water has a metallic or rusty color when first opened.
|
Corrosion / Rust Contamination | View Details |
| – |
Hot water has a strong rotten-egg (sulfur) smell.
|
Bacterial Contamination / Sulfide Reaction | View Details |
| – |
No hot water at any tap; the display is on, but the burner does not start and no error code is shown.
|
No Demand Detection / Flow Activation Failure | View Details |
| – |
The burner runs, but there is a strong smell of combustion or fumes near the heater.
|
Flue Gas Recirculation / Ventilation Problem | View Details |
| – |
The heater makes loud banging or knocking noises when starting or stopping.
|
Water Hammer / Delayed Ignition | View Details |
| – |
The pilot light will not stay lit on older Junkers pilot-type water heaters.
|
Pilot Flame Instability / Thermocouple Failure | View Details |
| – |
The water heater ignites, but hot water is only lukewarm even at the maximum temperature setting.
|
Insufficient Heating / Underfiring | View Details |
| – |
The water heater leaks from the flue condensate drain or around the flue connection.
|
Condensate / Flue Leak | View Details |
| – |
The water heater leaks water from the bottom of the casing.
|
Internal Water Leak | View Details |
| – |
Water heater emits a high-pitched whistling or humming noise during operation.
|
Acoustic Resonance / Flow Noise | View Details |
| – |
Water heater frequently shuts off due to overpressure, discharging water from the safety valve.
|
Overpressure / Expansion Control Problem | View Details |
| – |
Water heater starts but shuts off when another tap is opened or closed, causing temperature shocks.
|
Flow Interaction / Hydraulic Imbalance | View Details |
| – |
Water temperature fluctuates between hot and cold during a shower.
|
Temperature Instability / Cycling | View Details |
No matching codes found
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