Vaillant Boiler Error Codes – Expert Troubleshooting Guide

Is your Vaillant boiler displaying an "F" fault code and stopped working? Don't panic. Many common issues, such as low water pressure or ignition failure, can often be identified and sometimes resolved without a full service call. This Termix.ro guide explains the most frequent error codes for ecoTEC, atmoTEC, and turboTEC models, helping you restore your home's comfort quickly.

📋 Most Common Vaillant Fault Codes (Table)

Fault Code	Meaning	Possible Cause	Recommended Action
F.22	Low Water Pressure	Leak in system or air in radiators	Check the pressure gauge; refill to 1.5 bar
F.28	Ignition Failure	No gas supply or faulty electrode	Check gas valve; press the Reset button
F.29	Flame Extinguished	Gas supply interrupted during use	Check gas meter/regulator or flue blockage
F.75	Pressure Sensor Fault	Blocked pump or dirty sensor	Requires a professional technician check
F.27	Spurious Flame	Moisture on electronics or faulty ionisation	Dry the area or call a technician

💡 How to Reset a Vaillant Boiler

If your boiler is locked out, locate the Reset button on the control panel. It is usually marked with a crossed-out flame symbol or the word "Reset".

Press and hold the button for 1–3 seconds.
The boiler will attempt to restart.

Note: If the error code reappears immediately, do not attempt multiple resets. This indicates a hardware fault that requires a professional inspection.

🛠️ Vaillant Boiler Fault Codes (F-Series)

Code English Description Possible Causes

F.00 Flow temperature sensor (NTC) interruption Faulty NTC, damaged cable, loose plug at NTC or electronics.

F.01 Return temperature sensor (NTC) interruption Faulty NTC, damaged cable, loose plug at NTC or electronics.

F.02 DHW (Domestic Hot Water) outlet sensor interruption Faulty NTC, damaged cable, loose plug.

F.03 Cylinder/Storage tank sensor interruption Faulty NTC, damaged cable, loose plug.

F.05 External flue gas sensor interruption Faulty sensor, disconnected plug, faulty cable.

F.06 Internal flue gas sensor interruption Faulty sensor, disconnected plug, faulty cable.

F.10 Flow temperature sensor short circuit Cable shorted to casing, faulty sensor.

F.11 Return temperature sensor short circuit Cable shorted to casing, faulty sensor.

F.12 DHW outlet sensor short circuit Cable shorted to casing, faulty sensor.

F.13 Cylinder sensor short circuit Cable shorted to casing, faulty sensor.

F.15 External flue gas sensor short circuit Cable shorted to casing, faulty sensor.

F.16 Internal flue gas sensor short circuit Cable shorted to casing, faulty sensor.

F.20 Safety temperature limiter triggered Overheating in the appliance.

F.22 Dry fire / Low water operation Low water level, blocked/faulty pump, faulty pump cable.

F.23 Water shortage (High flow/return ΔT) Blocked pump, low pump output, faulty cable.

F.24 Water shortage (Temp rise too fast) Blocked pump, air in system, low system pressure.

F.25 Compact thermal module wiring interruption Wiring harness failure.

F.26 Gas valve stepper motor current implausible Disconnected motor, faulty gas valve, faulty PCB.

F.27 External light (False flame signal) Moisture in combustion chamber, faulty ionization electrode.

F.28 Ignition failure (Start-up attempt failed) Gas supply error, dirty combustion chamber, faulty ignition.

F.29 Flame failure during operation Gas supply interrupted, improper grounding.

F.32 Fan speed deviation Blocked fan, loose plug, faulty Hall sensor, PCB error.

F.36 Flue gas spillage detected Blocked flue, insufficient air intake, downdraught.

F.46 Short circuit: Solar circuit water sensor Faulty sensor, short in wiring harness/casing.

F.49 eBUS secondary voltage detection eBUS short circuit, overload, or reverse polarity.

F.61 Gas valve control error Short circuit to ground in wiring, faulty gas valve/PCB.

F.62 Gas valve shut-off delay failure Dirty burner, leaking gas valve, faulty electronics.

F.63 EEPROM error Faulty main electronics (PCB).

F.64 Electronics/Sensor fault Flow/Return sensor short or PCB failure.

F.65 Electronics temperature too high External heat influence or faulty PCB.

F.67 Flame control relay signal out of range Faulty electronics.

F.68 Unstable flame (Analog input) Air in gas, low gas pressure, faulty ionization electrode.

F.70 Device variant mismatch (Display/PCB) Display and PCB replaced simultaneously without coding.

F.71 Flow sensor constant value Faulty sensor, wiring, or electronics.

F.72 Flow/Return sensor error Faulty sensors, wiring, or faulty PCB.

F.73 Water pressure sensor error Disconnected plug, faulty wiring.

F.74 Water pressure sensor error (Internal) Internal sensor failure.

F.75 Pressure pump jump not detected Faulty pressure sensor, faulty pump, air in system.

F.76 Overheating protection (Heat exchanger) Thermal fuse triggered or faulty heat exchanger.

F.77 Flue gas damper fault Damper connection or component failure.

F.83 Burner temperature sensor error Sensor fault, air in system, sensor not seated correctly.

F.84 Flow/Return sensor error (ΔT < -6 K) Sensors swapped or incorrectly mounted.

F.85 Temperature sensor error Sensors mounted on the wrong pipe or not connected.

F.87 Ignition electrode fault Disconnected, short circuit in wiring.

F.88 Gas valve fault Disconnected, short circuit in wiring.

F.89 Pump fault Disconnected, short circuit in wiring.

🛰️ Advanced Diagnostics (F.090+)

F.090: Internal cylinder communication interrupted. Check wiring and PCB plugs.

F.092: Gas type conversion failed. Check settings in D.156.

F.095: Gas valve stepper motor reached minimum steps. Check flue path, condensate drain, or gas type.

F.096: Gas valve stepper motor reached maximum steps. Low gas inlet pressure or faulty PCB.

F.105: Gas valve offset adjustment required. Check settings in D.052 and D.182.

F.194: PCB power supply unit faulty. Replace PCB.

F.195: Significant Undervoltage detected. Check mains voltage (contact utility provider if necessary).

F.196: Significant Overvoltage detected. Check mains voltage.

F.317: DHW flow sensor signal implausible. Check sensor plug and wiring.

F.318: Motorized 3-way valve failure. Check plug, wiring, or replace valve.

F.320: Heating pump blocked. Clean or replace pump.

F.322: Heating pump overheated. Check system temperatures.

F.323: Pump running dry. Bleed the air from the system.

F.326: Hydraulic test failure (Multiple components). Check 3-way valve and wiring.

F.346: Forced ignition failed. Air in gas pipe, flue blockage, or faulty electrode.

F.707: eBUS communication failure between display and PCB.

🔄 Reversible Emergency Codes (L-Series)

These codes indicate temporary issues where the system may still operate in a limited mode.

L.016: Flame out detected at minimum power.

L.022: Flow rate in heating circuit too low.

L.025: Cold water inlet sensor shorted.

L.105: Appliance not vented correctly. Venting program failed.

L.144: Ionization signal too low. Adjustment failed.

L.320: Pump blocked; appliance is attempting to clear the blockage.

🛑 Irreversible Emergency Codes (N-Series)

These codes require manual intervention or parts replacement.

N.013: Water pressure sensor signal invalid.

N.032: Flow sensor faulty or signal implausible.

N.089: Installed pump does not match appliance type.

N.100: External sensor signal interrupted. Check D.162 settings.

N.144: Ionization signal low; adjustment failed repeatedly.

📋 Test & Maintenance Programs

P.000: Purging/Venting program (Radiators and DHW).

P.001: Full load heating test.

P.008: Priority valve to mid-position (for filling/draining).

T.001–T.006: Actuator tests (Pump, 3-way valve, Fan, Charging pump).

I.003: Maintenance interval reached. Service required.

I.020: Low water pressure warning. Refill the system.

I.144: Control electrode aging warning. Replace electrode and reset values (D.146/147).

Code	English Description	Possible Causes
F.00	Flow temperature sensor (NTC) interruption	Faulty NTC, damaged cable, loose plug at NTC or electronics.
F.01	Return temperature sensor (NTC) interruption	Faulty NTC, damaged cable, loose plug at NTC or electronics.
F.02	DHW (Domestic Hot Water) outlet sensor interruption	Faulty NTC, damaged cable, loose plug.
F.03	Cylinder/Storage tank sensor interruption	Faulty NTC, damaged cable, loose plug.
F.05	External flue gas sensor interruption	Faulty sensor, disconnected plug, faulty cable.
F.06	Internal flue gas sensor interruption	Faulty sensor, disconnected plug, faulty cable.
F.10	Flow temperature sensor short circuit	Cable shorted to casing, faulty sensor.
F.11	Return temperature sensor short circuit	Cable shorted to casing, faulty sensor.
F.12	DHW outlet sensor short circuit	Cable shorted to casing, faulty sensor.
F.13	Cylinder sensor short circuit	Cable shorted to casing, faulty sensor.
F.15	External flue gas sensor short circuit	Cable shorted to casing, faulty sensor.
F.16	Internal flue gas sensor short circuit	Cable shorted to casing, faulty sensor.
F.20	Safety temperature limiter triggered	Overheating in the appliance.
F.22	Dry fire / Low water operation	Low water level, blocked/faulty pump, faulty pump cable.
F.23	Water shortage (High flow/return ΔT)	Blocked pump, low pump output, faulty cable.
F.24	Water shortage (Temp rise too fast)	Blocked pump, air in system, low system pressure.
F.25	Compact thermal module wiring interruption	Wiring harness failure.
F.26	Gas valve stepper motor current implausible	Disconnected motor, faulty gas valve, faulty PCB.
F.27	External light (False flame signal)	Moisture in combustion chamber, faulty ionization electrode.
F.28	Ignition failure (Start-up attempt failed)	Gas supply error, dirty combustion chamber, faulty ignition.
F.29	Flame failure during operation	Gas supply interrupted, improper grounding.
F.32	Fan speed deviation	Blocked fan, loose plug, faulty Hall sensor, PCB error.
F.36	Flue gas spillage detected	Blocked flue, insufficient air intake, downdraught.
F.46	Short circuit: Solar circuit water sensor	Faulty sensor, short in wiring harness/casing.
F.49	eBUS secondary voltage detection	eBUS short circuit, overload, or reverse polarity.
F.61	Gas valve control error	Short circuit to ground in wiring, faulty gas valve/PCB.
F.62	Gas valve shut-off delay failure	Dirty burner, leaking gas valve, faulty electronics.
F.63	EEPROM error	Faulty main electronics (PCB).
F.64	Electronics/Sensor fault	Flow/Return sensor short or PCB failure.
F.65	Electronics temperature too high	External heat influence or faulty PCB.
F.67	Flame control relay signal out of range	Faulty electronics.
F.68	Unstable flame (Analog input)	Air in gas, low gas pressure, faulty ionization electrode.
F.70	Device variant mismatch (Display/PCB)	Display and PCB replaced simultaneously without coding.
F.71	Flow sensor constant value	Faulty sensor, wiring, or electronics.
F.72	Flow/Return sensor error	Faulty sensors, wiring, or faulty PCB.
F.73	Water pressure sensor error	Disconnected plug, faulty wiring.
F.74	Water pressure sensor error (Internal)	Internal sensor failure.
F.75	Pressure pump jump not detected	Faulty pressure sensor, faulty pump, air in system.
F.76	Overheating protection (Heat exchanger)	Thermal fuse triggered or faulty heat exchanger.
F.77	Flue gas damper fault	Damper connection or component failure.
F.83	Burner temperature sensor error	Sensor fault, air in system, sensor not seated correctly.
F.84	Flow/Return sensor error (ΔT < -6 K)	Sensors swapped or incorrectly mounted.
F.85	Temperature sensor error	Sensors mounted on the wrong pipe or not connected.
F.87	Ignition electrode fault	Disconnected, short circuit in wiring.
F.88	Gas valve fault	Disconnected, short circuit in wiring.
F.89	Pump fault	Disconnected, short circuit in wiring.

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