Vaillant 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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F.00
Water heater does not start; display shows F.00 and burner never ignites.
Flow Temperature Sensor Open Circuit
F.01
Water heater locks out with F.01; unit attempts to start but shuts down quickly.
Flow Temperature Sensor Short Circuit
F.10
Display shows F.10; water heater will not fire when hot water is demanded.
Return Temperature Sensor Open Circuit
F.11
F.11 displayed; unit may start briefly then shut down, or not start at all.
Return Temperature Sensor Short Circuit
F.20
Water heater locks out with F.20; unit overheats and shuts down, sometimes with very hot water at outlets
Safety Temperature Limiter / Overheat Protection Activated
F.22
F.22 displayed; water heater will not fire, sometimes accompanied by gurgling noises
Dry Fire / Low Water Pressure / No Water in Heat Exchanger
F.23
F.23 error; unit may start then quickly shut down, often with noisy operation
Flow/Return Temperature Difference Too High (Low Circulation)
F.24
F.24 displayed; rapid temperature rise detected, unit shuts down quickly
Rapid Temperature Rise / Low Water Content
F.28
F.28 ignition fault; water heater attempts to ignite several times but fails, no stable flame
Ignition Failure / No Flame Establishment
F.29
F.29 flame loss; burner lights briefly then goes out, unit locks out
Flame Detection Failure / Flame Loss During Operation
F.32
F.32 displayed; fan does not run or runs erratically, no ignition
Fan Motor Fault / Fan Speed Signal Error
F.33
F.33 air/flue fault; appliance does not ignite or shuts down shortly after starting
Air Pressure Switch / Flue Gas Path Fault
F.36
F.36 flue gas recirculation; appliance shuts down shortly after ignition
Flue Gas Recirculation / Flue Blockage
F.61
F.61 gas valve fault; appliance will not ignite
Gas Valve Control Fault
F.62
F.62 gas valve closing fault; the appliance may continue burning briefly after demand ends or lock out.
Delayed Gas Valve Closure / Gas Valve Sticking
F.64
F.64 electronics temperature fault; the appliance may shut down intermittently.
Electronics Overtemperature / Sensor Fault
F.65
F.65 electronics fault; the appliance is locked out and will not operate.
Electronics Overtemperature / PCB Protection Triggered
F.67
F.67 flame signal error; the appliance locks out after failed ignition attempts.
Flame Signal Processing Fault
F.70
F.70 displayed after PCB replacement or power-up; the appliance may not operate correctly.
Configuration / Appliance Type Mismatch
F.71
F.71 temperature sensor plausibility error; the appliance may cycle rapidly or shut down.
Flow Temperature Sensor Plausibility Fault
F.72
F.72 flow/return sensor mismatch; the appliance may not modulate correctly.
Flow and Return Temperature Sensor Difference Implausible
F.75
F.75 pump/flow detection fault; the appliance does not start the heating cycle.
No Pressure Change Detected on Pump Start (where fitted)
F.76
F.76 primary heat exchanger overheat; the appliance is locked out.
Primary Heat Exchanger Thermal Fuse Triggered
F.83
F.83 temperature rise fault; the appliance may start but quickly shut down.
Insufficient Water Flow / Incorrect Temperature Rise
F.84
F.84 flow sensor plausibility fault; temperature control unstable
Flow Sensor / NTC Correlation Error
F.85
F.85 multiple flow sensor fault; appliance may not respond correctly to demand
Flow Sensor Signal Error / Multiple Sensors Conflict
F.91
F.91 gas type / combustion fault; appliance may run roughly or shut down
Gas Type / Combustion Configuration Error
Symptom
Water heater delivers hot water initially, then the temperature quickly drops to lukewarm or cold
Intermittent DHW Temperature / Flow Modulation Fault
Symptom
Water heater emits a burning smell or plastic smell during operation
Overheating Electrical Component / Insulation Damage
Symptom
Water heater frequently cycles on and off with short burner run times.
Short Cycling / Control Instability.
Symptom
Water heater is leaking from the condensate pipe or trap area
Condensate Drain Leak / Blockage
Symptom
Water heater is leaking water from the bottom of the casing
Internal Water Leak
Symptom
Water heater is unusually noisy, with humming or grinding sounds during operation.
Mechanical Noise from Pump, Fan, or Burner.
Symptom
Water heater makes loud banging or knocking noises when heating water
Kettling / Boiling in Heat Exchanger
Symptom
Water heater produces no hot water at any tap, but the display shows no error code
No DHW Production Without Fault Code
Symptom
Water heater temperature fluctuates between very hot and cold during a shower
DHW Temperature Instability
Symptom
Water heater trips the electrical breaker or RCD when it starts.
Electrical Short or Earth Leakage.
Symptom
Water heater vibrates excessively or rattles when the burner is running.
Vibration / Resonance Fault.
Symptom
Water heater will not power on at all; display is blank.
No Power / Dead Appliance.
Symptom
Water heater's flue terminal shows signs of staining or water dripping.
Condensate / Flue Gas Discharge Issue.
Symptom
Water heater's hot water is not hot enough even at maximum setting.
Underheating DHW / Insufficient Output.
Symptom
Water heater's hot water is too hot even at low temperature setting.
Overheating DHW / Temperature Control Fault.
Symptom
Water heater's hot water output is lower than expected (reduced flow rate).
Reduced DHW Flow / Hydraulic Restriction.
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| F.00 |
Water heater does not start; display shows F.00 and burner never ignites.
|
Flow Temperature Sensor Open Circuit | View Details |
| F.01 |
Water heater locks out with F.01; unit attempts to start but shuts down quickly.
|
Flow Temperature Sensor Short Circuit | View Details |
| F.10 |
Display shows F.10; water heater will not fire when hot water is demanded.
|
Return Temperature Sensor Open Circuit | View Details |
| F.11 |
F.11 displayed; unit may start briefly then shut down, or not start at all.
|
Return Temperature Sensor Short Circuit | View Details |
| F.20 |
Water heater locks out with F.20; unit overheats and shuts down, sometimes with very hot water at outlets
|
Safety Temperature Limiter / Overheat Protection Activated | View Details |
| F.22 |
F.22 displayed; water heater will not fire, sometimes accompanied by gurgling noises
|
Dry Fire / Low Water Pressure / No Water in Heat Exchanger | View Details |
| F.23 |
F.23 error; unit may start then quickly shut down, often with noisy operation
|
Flow/Return Temperature Difference Too High (Low Circulation) | View Details |
| F.24 |
F.24 displayed; rapid temperature rise detected, unit shuts down quickly
|
Rapid Temperature Rise / Low Water Content | View Details |
| F.28 |
F.28 ignition fault; water heater attempts to ignite several times but fails, no stable flame
|
Ignition Failure / No Flame Establishment | View Details |
| F.29 |
F.29 flame loss; burner lights briefly then goes out, unit locks out
|
Flame Detection Failure / Flame Loss During Operation | View Details |
| F.32 |
F.32 displayed; fan does not run or runs erratically, no ignition
|
Fan Motor Fault / Fan Speed Signal Error | View Details |
| F.33 |
F.33 air/flue fault; appliance does not ignite or shuts down shortly after starting
|
Air Pressure Switch / Flue Gas Path Fault | View Details |
| F.36 |
F.36 flue gas recirculation; appliance shuts down shortly after ignition
|
Flue Gas Recirculation / Flue Blockage | View Details |
| F.61 |
F.61 gas valve fault; appliance will not ignite
|
Gas Valve Control Fault | View Details |
| F.62 |
F.62 gas valve closing fault; the appliance may continue burning briefly after demand ends or lock out.
|
Delayed Gas Valve Closure / Gas Valve Sticking | View Details |
| F.64 |
F.64 electronics temperature fault; the appliance may shut down intermittently.
|
Electronics Overtemperature / Sensor Fault | View Details |
| F.65 |
F.65 electronics fault; the appliance is locked out and will not operate.
|
Electronics Overtemperature / PCB Protection Triggered | View Details |
| F.67 |
F.67 flame signal error; the appliance locks out after failed ignition attempts.
|
Flame Signal Processing Fault | View Details |
| F.70 |
F.70 displayed after PCB replacement or power-up; the appliance may not operate correctly.
|
Configuration / Appliance Type Mismatch | View Details |
| F.71 |
F.71 temperature sensor plausibility error; the appliance may cycle rapidly or shut down.
|
Flow Temperature Sensor Plausibility Fault | View Details |
| F.72 |
F.72 flow/return sensor mismatch; the appliance may not modulate correctly.
|
Flow and Return Temperature Sensor Difference Implausible | View Details |
| F.75 |
F.75 pump/flow detection fault; the appliance does not start the heating cycle.
|
No Pressure Change Detected on Pump Start (where fitted) | View Details |
| F.76 |
F.76 primary heat exchanger overheat; the appliance is locked out.
|
Primary Heat Exchanger Thermal Fuse Triggered | View Details |
| F.83 |
F.83 temperature rise fault; the appliance may start but quickly shut down.
|
Insufficient Water Flow / Incorrect Temperature Rise | View Details |
| F.84 |
F.84 flow sensor plausibility fault; temperature control unstable
|
Flow Sensor / NTC Correlation Error | View Details |
| F.85 |
F.85 multiple flow sensor fault; appliance may not respond correctly to demand
|
Flow Sensor Signal Error / Multiple Sensors Conflict | View Details |
| F.91 |
F.91 gas type / combustion fault; appliance may run roughly or shut down
|
Gas Type / Combustion Configuration Error | View Details |
| – |
Water heater delivers hot water initially, then the temperature quickly drops to lukewarm or cold
|
Intermittent DHW Temperature / Flow Modulation Fault | View Details |
| – |
Water heater emits a burning smell or plastic smell during operation
|
Overheating Electrical Component / Insulation Damage | View Details |
| – |
Water heater frequently cycles on and off with short burner run times.
|
Short Cycling / Control Instability. | View Details |
| – |
Water heater is leaking from the condensate pipe or trap area
|
Condensate Drain Leak / Blockage | View Details |
| – |
Water heater is leaking water from the bottom of the casing
|
Internal Water Leak | View Details |
| – |
Water heater is unusually noisy, with humming or grinding sounds during operation.
|
Mechanical Noise from Pump, Fan, or Burner. | View Details |
| – |
Water heater makes loud banging or knocking noises when heating water
|
Kettling / Boiling in Heat Exchanger | View Details |
| – |
Water heater produces no hot water at any tap, but the display shows no error code
|
No DHW Production Without Fault Code | View Details |
| – |
Water heater temperature fluctuates between very hot and cold during a shower
|
DHW Temperature Instability | View Details |
| – |
Water heater trips the electrical breaker or RCD when it starts.
|
Electrical Short or Earth Leakage. | View Details |
| – |
Water heater vibrates excessively or rattles when the burner is running.
|
Vibration / Resonance Fault. | View Details |
| – |
Water heater will not power on at all; display is blank.
|
No Power / Dead Appliance. | View Details |
| – |
Water heater's flue terminal shows signs of staining or water dripping.
|
Condensate / Flue Gas Discharge Issue. | View Details |
| – |
Water heater's hot water is not hot enough even at maximum setting.
|
Underheating DHW / Insufficient Output. | View Details |
| – |
Water heater's hot water is too hot even at low temperature setting.
|
Overheating DHW / Temperature Control Fault. | View Details |
| – |
Water heater's hot water output is lower than expected (reduced flow rate).
|
Reduced DHW Flow / Hydraulic Restriction. | View Details |
No matching codes found
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