Buderus Water Heaters Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
Advertisements
A11
The unit displays A11 and will not operate; this may occur after a power interruption or wiring work.
Outdoor Temperature Sensor Fault (if equipped)
A21
The display shows A21; the burner shuts down, and the unit locks out after running for a short time.
Flue Gas Temperature Sensor Fault / Overtemperature
A41
The heater shows A41; the unit may not start or may shut down unexpectedly.
Flow Sensor / Flow Switch Fault
A51
Error A51 appears; the burner does not ignite or shuts down quickly.
DHW Temperature Sensor Fault (Storage Tank or Internal)
A61
The display shows A61; the unit may lock out and not respond to demand.
Internal Control Sensor / Safety Sensor Fault
A7
Water heater does not heat properly; the display shows A7, and the burner does not ignite or shuts down shortly after an ignition attempt.
Flow Temperature Sensor Fault
A71
Error A71 is displayed; the heater may run at reduced output or shut down.
Solar or Auxiliary Temperature Sensor Fault (if connected)
A8
Water heater shows A8 and will not start; the unit may attempt ignition and then lock out.
Return Temperature Sensor Fault
A81
The heater shows A81; the unit may not respond to thermostat or control commands.
Room Thermostat / EMS Bus Sensor Fault
A9
The display shows A9; water temperature fluctuates, or the unit shuts down intermittently.
DHW Outlet Temperature Sensor Fault
A91
Error A91 appears; the heater may operate erratically or not at all.
System Sensor / Additional NTC Fault
E0
The display shows E0; the heater is unresponsive or shuts down unexpectedly.
General Control Board Fault / Internal Error
E2
The water heater displays E2; the burner does not ignite and the unit locks out.
Flame Detection Fault
E3
The display shows E3; the unit fails to ignite or shuts down during the ignition sequence.
Ignition Failure
E9
The heater shows E9 and shuts down; the water may be very hot just before lockout.
Overheat / Safety Temperature Limiter Trip
EA
Error EA is displayed; the burner does not ignite or shuts down immediately after an ignition attempt.
No Flame Detected / Ignition Lockout
H11
The heater displays H11; the unit may continue to run but with limited functionality.
Communication Fault with Remote Controller
H12
Error H12 appears; the heater may not respond to external demand signals.
External Control Signal Fault
H13
Display shows H13; the heater may operate in a limited mode or not at all.
Sensor Configuration / Parameter Fault
H41
Heater shows H41; performance may be reduced, or the unit may shut down intermittently.
Fan Speed / Combustion Air Fault
H51
Error H51 displayed; the heater may shut down during operation.
Low Water Pressure / Flow Fault
H61
Heater shows H61; the unit may continue to run but with warnings.
Condensate Drain / Siphon Fault
H71
Error H71; the heater may not modulate correctly or may shut down.
Gas Valve Modulation / Control Fault
H81
Heater displays H81; the unit may run at reduced output or shut down.
Return Temperature Too High / Delta-T Fault
H91
Error H91; the heater may not start or may shut down unexpectedly.
Power Supply / Voltage Fault
Symptom
Hot water has a metallic or rusty color when first drawn from taps served by the Buderus water heater.
Corrosion / Rust Contamination
Symptom
The water heater display is on but unresponsive to button presses.
User Interface / Keypad Failure
Symptom
The water heater does not start at all; the display is blank and no lights are on.
No Power / Dead Unit
Symptom
The water heater fan runs, but the burner does not ignite, and no error code is shown.
Pre-Ignition Sequence Stalled
Symptom
The water heater frequently cycles on and off with short run times, even with steady hot water demand.
Short Cycling
Symptom
The water heater is leaking from the bottom of the unit.
Internal Water Leak
Symptom
The water heater makes loud banging or knocking noises during operation.
Kettling / Boiling in Heat Exchanger
Symptom
The water heater occasionally trips the building's residual current device (RCD) or ground fault interrupter.
Earth Leakage / Ground Fault
Symptom
The water heater runs but produces excessive white steam or vapor from the flue terminal.
Abnormal Combustion / Condensation Behavior
Symptom
The water heater vibrates excessively or rattles when the burner is running.
Mechanical Vibration / Mounting Issue
Symptom
The water heater's condensate drain repeatedly clogs, causing water to back up inside the unit.
Chronic Condensate Blockage
Symptom
The water heater's pressure relief valve frequently discharges water.
Overpressure / Overtemperature Relief Activation
Symptom
There is a strong burning or electrical smell coming from the water heater.
Overheating Electrical Component
Symptom
There is a strong gas smell near the Buderus water heater.
Gas Leak
Symptom
Water heater does not produce any hot water; the burner never starts, and no error code is displayed.
No Demand Recognition / Flow Detection Failure
Symptom
Water heater produces lukewarm water only; the temperature never reaches the setpoint.
Insufficient Burner Output / Modulation Issue
Symptom
Water temperature fluctuates between hot and cold during a shower, with no error code.
Temperature Control Instability
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| A11 |
The unit displays A11 and will not operate; this may occur after a power interruption or wiring work.
|
Outdoor Temperature Sensor Fault (if equipped) | View Details |
| A21 |
The display shows A21; the burner shuts down, and the unit locks out after running for a short time.
|
Flue Gas Temperature Sensor Fault / Overtemperature | View Details |
| A41 |
The heater shows A41; the unit may not start or may shut down unexpectedly.
|
Flow Sensor / Flow Switch Fault | View Details |
| A51 |
Error A51 appears; the burner does not ignite or shuts down quickly.
|
DHW Temperature Sensor Fault (Storage Tank or Internal) | View Details |
| A61 |
The display shows A61; the unit may lock out and not respond to demand.
|
Internal Control Sensor / Safety Sensor Fault | View Details |
| A7 |
Water heater does not heat properly; the display shows A7, and the burner does not ignite or shuts down shortly after an ignition attempt.
|
Flow Temperature Sensor Fault | View Details |
| A71 |
Error A71 is displayed; the heater may run at reduced output or shut down.
|
Solar or Auxiliary Temperature Sensor Fault (if connected) | View Details |
| A8 |
Water heater shows A8 and will not start; the unit may attempt ignition and then lock out.
|
Return Temperature Sensor Fault | View Details |
| A81 |
The heater shows A81; the unit may not respond to thermostat or control commands.
|
Room Thermostat / EMS Bus Sensor Fault | View Details |
| A9 |
The display shows A9; water temperature fluctuates, or the unit shuts down intermittently.
|
DHW Outlet Temperature Sensor Fault | View Details |
| A91 |
Error A91 appears; the heater may operate erratically or not at all.
|
System Sensor / Additional NTC Fault | View Details |
| E0 |
The display shows E0; the heater is unresponsive or shuts down unexpectedly.
|
General Control Board Fault / Internal Error | View Details |
| E2 |
The water heater displays E2; the burner does not ignite and the unit locks out.
|
Flame Detection Fault | View Details |
| E3 |
The display shows E3; the unit fails to ignite or shuts down during the ignition sequence.
|
Ignition Failure | View Details |
| E9 |
The heater shows E9 and shuts down; the water may be very hot just before lockout.
|
Overheat / Safety Temperature Limiter Trip | View Details |
| EA |
Error EA is displayed; the burner does not ignite or shuts down immediately after an ignition attempt.
|
No Flame Detected / Ignition Lockout | View Details |
| H11 |
The heater displays H11; the unit may continue to run but with limited functionality.
|
Communication Fault with Remote Controller | View Details |
| H12 |
Error H12 appears; the heater may not respond to external demand signals.
|
External Control Signal Fault | View Details |
| H13 |
Display shows H13; the heater may operate in a limited mode or not at all.
|
Sensor Configuration / Parameter Fault | View Details |
| H41 |
Heater shows H41; performance may be reduced, or the unit may shut down intermittently.
|
Fan Speed / Combustion Air Fault | View Details |
| H51 |
Error H51 displayed; the heater may shut down during operation.
|
Low Water Pressure / Flow Fault | View Details |
| H61 |
Heater shows H61; the unit may continue to run but with warnings.
|
Condensate Drain / Siphon Fault | View Details |
| H71 |
Error H71; the heater may not modulate correctly or may shut down.
|
Gas Valve Modulation / Control Fault | View Details |
| H81 |
Heater displays H81; the unit may run at reduced output or shut down.
|
Return Temperature Too High / Delta-T Fault | View Details |
| H91 |
Error H91; the heater may not start or may shut down unexpectedly.
|
Power Supply / Voltage Fault | View Details |
| – |
Hot water has a metallic or rusty color when first drawn from taps served by the Buderus water heater.
|
Corrosion / Rust Contamination | View Details |
| – |
The water heater display is on but unresponsive to button presses.
|
User Interface / Keypad Failure | View Details |
| – |
The water heater does not start at all; the display is blank and no lights are on.
|
No Power / Dead Unit | View Details |
| – |
The water heater fan runs, but the burner does not ignite, and no error code is shown.
|
Pre-Ignition Sequence Stalled | View Details |
| – |
The water heater frequently cycles on and off with short run times, even with steady hot water demand.
|
Short Cycling | View Details |
| – |
The water heater is leaking from the bottom of the unit.
|
Internal Water Leak | View Details |
| – |
The water heater makes loud banging or knocking noises during operation.
|
Kettling / Boiling in Heat Exchanger | View Details |
| – |
The water heater occasionally trips the building's residual current device (RCD) or ground fault interrupter.
|
Earth Leakage / Ground Fault | View Details |
| – |
The water heater runs but produces excessive white steam or vapor from the flue terminal.
|
Abnormal Combustion / Condensation Behavior | View Details |
| – |
The water heater vibrates excessively or rattles when the burner is running.
|
Mechanical Vibration / Mounting Issue | View Details |
| – |
The water heater's condensate drain repeatedly clogs, causing water to back up inside the unit.
|
Chronic Condensate Blockage | View Details |
| – |
The water heater's pressure relief valve frequently discharges water.
|
Overpressure / Overtemperature Relief Activation | View Details |
| – |
There is a strong burning or electrical smell coming from the water heater.
|
Overheating Electrical Component | View Details |
| – |
There is a strong gas smell near the Buderus water heater.
|
Gas Leak | View Details |
| – |
Water heater does not produce any hot water; the burner never starts, and no error code is displayed.
|
No Demand Recognition / Flow Detection Failure | View Details |
| – |
Water heater produces lukewarm water only; the temperature never reaches the setpoint.
|
Insufficient Burner Output / Modulation Issue | View Details |
| – |
Water temperature fluctuates between hot and cold during a shower, with no error code.
|
Temperature Control Instability | View Details |
No matching codes found
Advertisements