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; display shows A2 shortly after a hot water tap is opened.
Ignition Failure – No Flame Detected
A3
Unit attempts to start but shuts down with A3; fan may run briefly, 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; 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 setpoint then drops, with frequent cycling.
Outlet Temperature Control Fault
E3
E3 error; unit may shut down during operation, especially in windy conditions.
Flue Gas / Draft Fault
E5
E5 displayed; 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; 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; heater may start but then shut down, especially at low flow rates.
Gas Valve Modulation / Combustion Control Fault
H11
H11 or similar code; unit may limit maximum temperature or power.
Service Interval Reached / Maintenance Code
H7
H7 displayed; unit may still operate but with reduced performance or noisy combustion.
Maintenance Reminder / Combustion Quality Degradation
L0
Display shows L0 or similar low-temperature/anti-freeze indication; burner may fire briefly without hot water demand.
Frost Protection Operation
P1
P1 appears; heater may not respond to hot water demand or shows incorrect flow.
Flow Sensor Calibration / Low Flow Detection Error
P2
P2 displayed; unit may limit output temperature or shut down under high demand.
Maximum Temperature Limitation / Overload Protection
Symptom
Burner runs but there is a strong smell of combustion or fumes near the heater.
Flue Gas Recirculation / Ventilation Problem
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
Heater makes loud banging or knocking noises when starting or stopping.
Water Hammer / Delayed Ignition
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; display is on, but burner does not start and no error code is shown.
No Demand Detection / Flow Activation Failure
Symptom
Pilot light will not stay lit on older Junkers pilot-type water heaters.
Pilot Flame Instability / Thermocouple Failure
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 ignites but hot water is only lukewarm even at maximum temperature setting.
Insufficient Heating / Underfiring
Symptom
Water heater leaks from the flue condensate drain or around the flue connection.
Condensate / Flue Leak
Symptom
Water heater leaks water from the bottom of the casing.
Internal Water Leak
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; display shows A2 shortly after a hot water tap is opened.
|
Ignition Failure – No Flame Detected | View Details |
| A3 |
Unit attempts to start but shuts down with A3; fan may run briefly, 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; 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 setpoint then drops, with frequent cycling.
|
Outlet Temperature Control Fault | View Details |
| E3 |
E3 error; unit may shut down during operation, especially in windy conditions.
|
Flue Gas / Draft Fault | View Details |
| E5 |
E5 displayed; 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; 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; heater may start but then shut down, especially at low flow rates.
|
Gas Valve Modulation / Combustion Control Fault | View Details |
| H11 |
H11 or similar code; unit may limit maximum temperature or power.
|
Service Interval Reached / Maintenance Code | View Details |
| H7 |
H7 displayed; unit may still operate but with reduced performance or noisy combustion.
|
Maintenance Reminder / Combustion Quality Degradation | View Details |
| L0 |
Display shows L0 or similar low-temperature/anti-freeze indication; burner may fire briefly without hot water demand.
|
Frost Protection Operation | View Details |
| P1 |
P1 appears; heater may not respond to hot water demand or shows incorrect flow.
|
Flow Sensor Calibration / Low Flow Detection Error | View Details |
| P2 |
P2 displayed; unit may limit output temperature or shut down under high demand.
|
Maximum Temperature Limitation / Overload Protection | View Details |
| – |
Burner runs but there is a strong smell of combustion or fumes near the heater.
|
Flue Gas Recirculation / Ventilation Problem | 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 |
| – |
Heater makes loud banging or knocking noises when starting or stopping.
|
Water Hammer / Delayed Ignition | 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; display is on, but burner does not start and no error code is shown.
|
No Demand Detection / Flow Activation Failure | View Details |
| – |
Pilot light will not stay lit on older Junkers pilot-type water heaters.
|
Pilot Flame Instability / Thermocouple Failure | 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 ignites but hot water is only lukewarm even at maximum temperature setting.
|
Insufficient Heating / Underfiring | View Details |
| – |
Water heater leaks from the flue condensate drain or around the flue connection.
|
Condensate / Flue Leak | View Details |
| – |
Water heater leaks water from the bottom of the casing.
|
Internal Water Leak | 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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