Vaillant Boilers Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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F.00
The boiler locks out and displays F.00; there is no heating or hot water.
Flow Temperature Sensor Open Circuit
F.01
The boiler displays F.01 and shuts down; there is no heating or hot water.
Flow Temperature Sensor Short Circuit
F.10
The boiler shows F.10; there is no heating or hot water.
Return Temperature Sensor Open Circuit
F.11
The boiler displays F.11 and locks out.
Return Temperature Sensor Short Circuit
F.20
The boiler shows F.20 and shuts down; the casing may feel hot.
Safety Temperature Limiter Activated / Overheat
F.22
Boiler displays F.22, no heating or hot water, pressure gauge low.
Low Water Pressure / Dry Fire Protection
F.23
Boiler shows F.23, intermittent heating, pump noisy or very hot.
Water Shortage / Pump or Flow Fault
F.24
Boiler locks out with F.24 shortly after starting.
Rapid Temperature Rise / Flow Fault
F.25
Boiler shows F.25, burner shuts down, possible flue or fan noise.
Flue Gas Temperature Too High / Flue Gas Sensor Trip
F.26
Boiler displays F.26, no ignition, fan may run briefly.
Gas Valve Fault / Regulation Error
F.27
Boiler shows F.27, ignition attempt aborted.
Flame Detection Fault / False Flame Signal
F.28
Boiler displays F.28, repeated failed ignition, no flame established.
Ignition Failure / No Flame Detected
F.29
Boiler shows F.29 after starting then going out, intermittent hot water or heating.
Flame Loss During Operation
F.32
Boiler displays F.32, fan does not run or runs erratically.
Fan Motor Fault / No Fan Signal
F.33
Boiler shows F.33, fan runs but boiler does not ignite.
Air Pressure Switch / Differential Pressure Fault
F.49
Boiler displays F.49, controls unresponsive or intermittent.
Low Voltage / 24V DC Supply Fault
F.61
Boiler displays F.61, no ignition, gas valve error.
Gas Valve Control Fault
F.62
Boiler displays F.62, delayed shutdown of gas valve or valve sticking.
Gas Valve Shut-off Fault
F.63
Boiler displays F.63, will not start, sometimes after a power surge.
EEPROM / PCB Configuration Fault
F.64
Boiler displays F.64, temperature sensor or PCB error.
NTC / PCB Processing Fault
F.65
Boiler displays F.65, PCB temperature too high.
Electronics Overtemperature
F.67
Boiler displays F.67, ignition/flame signal error.
Flame Detection / PCB Fault
F.70
Boiler displays F.70 after PCB replacement or service.
Incompatible or Unconfigured PCB
F.72
Boiler displays F.72, inconsistent flow/return temperature readings.
Flow/Return NTC Mismatch
F.73
Boiler displays F.73, pressure reading too low or sensor open circuit.
Water Pressure Sensor Open Circuit
F.74
Boiler displays F.74: pressure reading too high or sensor short circuit.
Water Pressure Sensor Short Circuit
F.75
Boiler displays F.75: no pressure rise detected when pump starts.
Pump / Pressure Sensor Interaction Fault
F.76
Boiler displays F.76: immediate lockout, possible smell of overheating.
Primary Heat Exchanger Overtemperature / Thermal Fuse Trip
F.83
Boiler displays F.83 on start-up, especially after draining or a new installation.
Insufficient Water / Temperature Rise Fault
F.84
Boiler displays F.84: inconsistent flow sensor readings.
Flow Sensor / NTC Fault
F.85
Boiler displays F.85: return sensor plausibility fault.
Return Sensor / NTC Fault
F.91
Boiler displays F.91: hot water temperature control unstable on combi models.
DHW Flow Sensor / Turbine Fault
Symptom
Boiler display is on, but there is no response to heating or hot water demand.
Control Signal / Demand Fault
Symptom
Boiler fan runs continuously even when there is no demand
Fan Overrun / Control Fault
Symptom
Boiler flue dripping water externally or staining the wall.
Condensate / Flue Joint Leak
Symptom
Boiler frequently cycles on and off; rooms never reach the set temperature.
Short Cycling / Control or Sizing Issue
Symptom
Boiler frequently needs manual reset, with various intermittent fault codes
Intermittent Electrical / PCB or Sensor Fault
Symptom
Boiler leaking water from underneath the casing.
Internal Water Leak
Symptom
Boiler losing pressure daily, no visible leaks on radiators.
Chronic Pressure Loss
Symptom
Boiler making loud banging or kettling noises when heating.
Kettling / Localised Boiling in Heat Exchanger
Symptom
Boiler pressure rises rapidly when heating is on and discharges through the pressure relief valve.
Failed Expansion Vessel
Symptom
Boiler runs, but radiators do not get hot or are only lukewarm.
Poor Heating Circulation
Symptom
Boiler will not start at all; no display or lights.
No Power / Dead Boiler
Symptom
Condensate pipe dripping heavily, or boiler stops in freezing weather.
Condensate Drain / Frozen Condensate
Symptom
Hot water temperature fluctuates or runs hot then cold on a Vaillant combi boiler.
Unstable Domestic Hot Water Temperature
Symptom
Radiators get hot when only hot water is requested on a Vaillant combi.
Diverter Valve Passing / Stuck Mid-Position
Symptom
Strong smell of gas near the Vaillant boiler.
Gas Leak
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| F.00 |
The boiler locks out and displays F.00; there is no heating or hot water.
|
Flow Temperature Sensor Open Circuit | View Details |
| F.01 |
The boiler displays F.01 and shuts down; there is no heating or hot water.
|
Flow Temperature Sensor Short Circuit | View Details |
| F.10 |
The boiler shows F.10; there is no heating or hot water.
|
Return Temperature Sensor Open Circuit | View Details |
| F.11 |
The boiler displays F.11 and locks out.
|
Return Temperature Sensor Short Circuit | View Details |
| F.20 |
The boiler shows F.20 and shuts down; the casing may feel hot.
|
Safety Temperature Limiter Activated / Overheat | View Details |
| F.22 |
Boiler displays F.22, no heating or hot water, pressure gauge low.
|
Low Water Pressure / Dry Fire Protection | View Details |
| F.23 |
Boiler shows F.23, intermittent heating, pump noisy or very hot.
|
Water Shortage / Pump or Flow Fault | View Details |
| F.24 |
Boiler locks out with F.24 shortly after starting.
|
Rapid Temperature Rise / Flow Fault | View Details |
| F.25 |
Boiler shows F.25, burner shuts down, possible flue or fan noise.
|
Flue Gas Temperature Too High / Flue Gas Sensor Trip | View Details |
| F.26 |
Boiler displays F.26, no ignition, fan may run briefly.
|
Gas Valve Fault / Regulation Error | View Details |
| F.27 |
Boiler shows F.27, ignition attempt aborted.
|
Flame Detection Fault / False Flame Signal | View Details |
| F.28 |
Boiler displays F.28, repeated failed ignition, no flame established.
|
Ignition Failure / No Flame Detected | View Details |
| F.29 |
Boiler shows F.29 after starting then going out, intermittent hot water or heating.
|
Flame Loss During Operation | View Details |
| F.32 |
Boiler displays F.32, fan does not run or runs erratically.
|
Fan Motor Fault / No Fan Signal | View Details |
| F.33 |
Boiler shows F.33, fan runs but boiler does not ignite.
|
Air Pressure Switch / Differential Pressure Fault | View Details |
| F.49 |
Boiler displays F.49, controls unresponsive or intermittent.
|
Low Voltage / 24V DC Supply Fault | View Details |
| F.61 |
Boiler displays F.61, no ignition, gas valve error.
|
Gas Valve Control Fault | View Details |
| F.62 |
Boiler displays F.62, delayed shutdown of gas valve or valve sticking.
|
Gas Valve Shut-off Fault | View Details |
| F.63 |
Boiler displays F.63, will not start, sometimes after a power surge.
|
EEPROM / PCB Configuration Fault | View Details |
| F.64 |
Boiler displays F.64, temperature sensor or PCB error.
|
NTC / PCB Processing Fault | View Details |
| F.65 |
Boiler displays F.65, PCB temperature too high.
|
Electronics Overtemperature | View Details |
| F.67 |
Boiler displays F.67, ignition/flame signal error.
|
Flame Detection / PCB Fault | View Details |
| F.70 |
Boiler displays F.70 after PCB replacement or service.
|
Incompatible or Unconfigured PCB | View Details |
| F.72 |
Boiler displays F.72, inconsistent flow/return temperature readings.
|
Flow/Return NTC Mismatch | View Details |
| F.73 |
Boiler displays F.73, pressure reading too low or sensor open circuit.
|
Water Pressure Sensor Open Circuit | View Details |
| F.74 |
Boiler displays F.74: pressure reading too high or sensor short circuit.
|
Water Pressure Sensor Short Circuit | View Details |
| F.75 |
Boiler displays F.75: no pressure rise detected when pump starts.
|
Pump / Pressure Sensor Interaction Fault | View Details |
| F.76 |
Boiler displays F.76: immediate lockout, possible smell of overheating.
|
Primary Heat Exchanger Overtemperature / Thermal Fuse Trip | View Details |
| F.83 |
Boiler displays F.83 on start-up, especially after draining or a new installation.
|
Insufficient Water / Temperature Rise Fault | View Details |
| F.84 |
Boiler displays F.84: inconsistent flow sensor readings.
|
Flow Sensor / NTC Fault | View Details |
| F.85 |
Boiler displays F.85: return sensor plausibility fault.
|
Return Sensor / NTC Fault | View Details |
| F.91 |
Boiler displays F.91: hot water temperature control unstable on combi models.
|
DHW Flow Sensor / Turbine Fault | View Details |
| – |
Boiler display is on, but there is no response to heating or hot water demand.
|
Control Signal / Demand Fault | View Details |
| – |
Boiler fan runs continuously even when there is no demand
|
Fan Overrun / Control Fault | View Details |
| – |
Boiler flue dripping water externally or staining the wall.
|
Condensate / Flue Joint Leak | View Details |
| – |
Boiler frequently cycles on and off; rooms never reach the set temperature.
|
Short Cycling / Control or Sizing Issue | View Details |
| – |
Boiler frequently needs manual reset, with various intermittent fault codes
|
Intermittent Electrical / PCB or Sensor Fault | View Details |
| – |
Boiler leaking water from underneath the casing.
|
Internal Water Leak | View Details |
| – |
Boiler losing pressure daily, no visible leaks on radiators.
|
Chronic Pressure Loss | View Details |
| – |
Boiler making loud banging or kettling noises when heating.
|
Kettling / Localised Boiling in Heat Exchanger | View Details |
| – |
Boiler pressure rises rapidly when heating is on and discharges through the pressure relief valve.
|
Failed Expansion Vessel | View Details |
| – |
Boiler runs, but radiators do not get hot or are only lukewarm.
|
Poor Heating Circulation | View Details |
| – |
Boiler will not start at all; no display or lights.
|
No Power / Dead Boiler | View Details |
| – |
Condensate pipe dripping heavily, or boiler stops in freezing weather.
|
Condensate Drain / Frozen Condensate | View Details |
| – |
Hot water temperature fluctuates or runs hot then cold on a Vaillant combi boiler.
|
Unstable Domestic Hot Water Temperature | View Details |
| – |
Radiators get hot when only hot water is requested on a Vaillant combi.
|
Diverter Valve Passing / Stuck Mid-Position | View Details |
| – |
Strong smell of gas near the Vaillant boiler.
|
Gas Leak | View Details |
No matching codes found
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