Viessmann 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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A1
A1 warning, unit continues to operate but with reduced performance
Limescale / Heat Exchanger Efficiency Warning
A2
A2 warning, unit indicates low but not critical water pressure
Low System Pressure Warning
A3
A3 warning, fan speed or combustion values out of optimal range but unit still runs
Combustion Optimization Warning
F1
Water heater locks out with F1 on display, burner does not start
Flame Detection Fault
F10
F10 displayed, unit will not start, often after power disturbances
Control Board / Internal Electronics Fault
F11
F11 error, unit indicates communication problem between display and main board
Internal Communication Fault
F12
F12 displayed, unit stops, often associated with sensor wiring issues
Sensor Circuit Short or Open
F13
F13 error, unit indicates low water pressure or lack of water in system
Water Pressure / Low Water Fault
F14
F14 displayed, burner shuts down due to high limit trip
Safety High-Limit Thermostat Trip
F15
F15 error, unit indicates condensate or drainage problem
Condensate Drain Fault
F16
F16 displayed, unit reports flue gas recirculation or combustion air fault
Combustion Air / Flue Recirculation Fault
F17
F17 error, unit indicates power supply or frequency issue
Mains Supply Fault
F18
F18 displayed, unit indicates sensor calibration or configuration error
Configuration / Parameter Fault
F2
Unit attempts to ignite but fails, F2 ignition fault displayed
Ignition Failure
F3
Water heater shuts down with F3, burner stops shortly after ignition
Flame Loss During Operation
F4
Display shows F4, unit does not start, fan may run briefly
Exhaust / Flue Gas Temperature Fault
F5
F5 error, unit shuts down during operation, often associated with overheating
Primary Heat Exchanger Overheat
F6
F6 displayed, water heater will not fire, fan may not start
Fan / Air Proving Fault
F7
F7 error, unit reports gas valve or gas supply problem, no ignition
Gas Valve / Gas Supply Fault
F8
F8 displayed, unit shuts down, often accompanied by high outlet temperature
Domestic Hot Water Temperature Sensor Fault
F9
F9 error, unit locks out, may occur intermittently during operation
Flow Sensor / Flow Switch Fault
Symptom
Burning plastic or electrical smell from the water heater casing
Overheating Electrical Component
Symptom
Display works but buttons or rotary knob do not respond
User Interface Input Failure
Symptom
High-pitched whistling or howling noise from the water heater during operation
Combustion or Flow-Induced Whistle
Symptom
Hot water temperature fluctuates between hot and cold during a shower
DHW Temperature Fluctuation
Symptom
Smell of exhaust fumes or burning around the water heater
Flue Gas Leakage
Symptom
Strong smell of gas near the water heater, no error code displayed
Gas Leak at Appliance
Symptom
Water dripping from the flue or condensate pipe connection
Condensate / Flue Leak
Symptom
Water heater does not produce any hot water, display is on and no error code is shown
No Hot Water Without Fault Code
Symptom
Water heater frequently loses pressure on the primary (heating) side, requiring regular top-ups
Chronic Pressure Loss
Symptom
Water heater is leaking water from the bottom of the casing
Internal Water Leak
Symptom
Water heater makes loud banging or knocking noises when burner starts or stops
Water Hammer / Thermal Expansion Noise
Symptom
Water heater produces lukewarm water only, cannot reach set temperature
Insufficient DHW Heating
Symptom
Water heater repeatedly turns on and off rapidly when hot water is used
Short Cycling on DHW Demand
Symptom
Water heater runs but gas consumption seems unusually high
Inefficient Combustion / Heat Loss
Symptom
Water heater takes a long time to deliver hot water to taps
Delayed Hot Water Delivery
Symptom
Water heater trips the household circuit breaker or RCD when it starts
Electrical Short or Earth Leakage
Symptom
Water heater vibrates excessively or rattles when running
Mechanical Vibration / Fan Imbalance
Symptom
Water heater will not power on, display is blank
No Power to Appliance
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| A1 |
A1 warning, unit continues to operate but with reduced performance
|
Limescale / Heat Exchanger Efficiency Warning | View Details |
| A2 |
A2 warning, unit indicates low but not critical water pressure
|
Low System Pressure Warning | View Details |
| A3 |
A3 warning, fan speed or combustion values out of optimal range but unit still runs
|
Combustion Optimization Warning | View Details |
| F1 |
Water heater locks out with F1 on display, burner does not start
|
Flame Detection Fault | View Details |
| F10 |
F10 displayed, unit will not start, often after power disturbances
|
Control Board / Internal Electronics Fault | View Details |
| F11 |
F11 error, unit indicates communication problem between display and main board
|
Internal Communication Fault | View Details |
| F12 |
F12 displayed, unit stops, often associated with sensor wiring issues
|
Sensor Circuit Short or Open | View Details |
| F13 |
F13 error, unit indicates low water pressure or lack of water in system
|
Water Pressure / Low Water Fault | View Details |
| F14 |
F14 displayed, burner shuts down due to high limit trip
|
Safety High-Limit Thermostat Trip | View Details |
| F15 |
F15 error, unit indicates condensate or drainage problem
|
Condensate Drain Fault | View Details |
| F16 |
F16 displayed, unit reports flue gas recirculation or combustion air fault
|
Combustion Air / Flue Recirculation Fault | View Details |
| F17 |
F17 error, unit indicates power supply or frequency issue
|
Mains Supply Fault | View Details |
| F18 |
F18 displayed, unit indicates sensor calibration or configuration error
|
Configuration / Parameter Fault | View Details |
| F2 |
Unit attempts to ignite but fails, F2 ignition fault displayed
|
Ignition Failure | View Details |
| F3 |
Water heater shuts down with F3, burner stops shortly after ignition
|
Flame Loss During Operation | View Details |
| F4 |
Display shows F4, unit does not start, fan may run briefly
|
Exhaust / Flue Gas Temperature Fault | View Details |
| F5 |
F5 error, unit shuts down during operation, often associated with overheating
|
Primary Heat Exchanger Overheat | View Details |
| F6 |
F6 displayed, water heater will not fire, fan may not start
|
Fan / Air Proving Fault | View Details |
| F7 |
F7 error, unit reports gas valve or gas supply problem, no ignition
|
Gas Valve / Gas Supply Fault | View Details |
| F8 |
F8 displayed, unit shuts down, often accompanied by high outlet temperature
|
Domestic Hot Water Temperature Sensor Fault | View Details |
| F9 |
F9 error, unit locks out, may occur intermittently during operation
|
Flow Sensor / Flow Switch Fault | View Details |
| – |
Burning plastic or electrical smell from the water heater casing
|
Overheating Electrical Component | View Details |
| – |
Display works but buttons or rotary knob do not respond
|
User Interface Input Failure | View Details |
| – |
High-pitched whistling or howling noise from the water heater during operation
|
Combustion or Flow-Induced Whistle | View Details |
| – |
Hot water temperature fluctuates between hot and cold during a shower
|
DHW Temperature Fluctuation | View Details |
| – |
Smell of exhaust fumes or burning around the water heater
|
Flue Gas Leakage | View Details |
| – |
Strong smell of gas near the water heater, no error code displayed
|
Gas Leak at Appliance | View Details |
| – |
Water dripping from the flue or condensate pipe connection
|
Condensate / Flue Leak | View Details |
| – |
Water heater does not produce any hot water, display is on and no error code is shown
|
No Hot Water Without Fault Code | View Details |
| – |
Water heater frequently loses pressure on the primary (heating) side, requiring regular top-ups
|
Chronic Pressure Loss | View Details |
| – |
Water heater is leaking water from the bottom of the casing
|
Internal Water Leak | View Details |
| – |
Water heater makes loud banging or knocking noises when burner starts or stops
|
Water Hammer / Thermal Expansion Noise | View Details |
| – |
Water heater produces lukewarm water only, cannot reach set temperature
|
Insufficient DHW Heating | View Details |
| – |
Water heater repeatedly turns on and off rapidly when hot water is used
|
Short Cycling on DHW Demand | View Details |
| – |
Water heater runs but gas consumption seems unusually high
|
Inefficient Combustion / Heat Loss | View Details |
| – |
Water heater takes a long time to deliver hot water to taps
|
Delayed Hot Water Delivery | View Details |
| – |
Water heater trips the household circuit breaker or RCD when it starts
|
Electrical Short or Earth Leakage | View Details |
| – |
Water heater vibrates excessively or rattles when running
|
Mechanical Vibration / Fan Imbalance | View Details |
| – |
Water heater will not power on, display is blank
|
No Power to Appliance | View Details |
No matching codes found
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