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