Why errors appear on Vaillant gas boilers and what they mean

Unlike the old gas appliances from the middle of the last century, which had primitive mechanical automation, modern heating boilers rely entirely on electrics and electronics during operation. They are equipped with a variety of sensors, electric drives of individual units and "smart" electronic control units. This allows you to react flexibly to temperature changes, load fluctuations and user commands. But at the same time, no gas boiler is 100% reliable. Voltage surges and dips, gas pressure pulsations, carbon deposits on sensors and scale deposits on heat exchangers or blockages that block the operation of actuators or individual systems can cause the device to “feel bad”. Vaillant gas boilers have a built-in self-diagnosis system for this case. By analyzing the readings of the sensors, it recognizes various types of failures and malfunctions and intrusively informs users about them by “winking” the display.

Error codes for Vaillant boilers of previous generations

Vaillant gas boilers, like heating installations of many other brands, display error messages on the main display of the device. When a failure occurs or a malfunction occurs, the boiler, instead of basic information (temperature in the circuit or working pressure in the system), displays a conditional code on the LCD screen, indicating a particular problem. Since there is not much space on the screen, Vaillant boilers report failures and malfunctions in the form of a very short code, which consists of the letter F and two numbers.

Boiler control panel Vaillant turboTEC pro.

The information on error codes given in this section is valid for conventional wall-mounted gas boilers Vaillant atmoTEC plus(with indices VU and VUW) and Vaillant turboTEC plus(with indices VU and VUW), Vaillant ecoTEC pure condensing units (with index VUW) , as well as Vaillant floor - standing condensing boilers of the ecoVIT, ecoVIT exclusiv, auroCOMPACT and ecoCOMPACT series. Since the table is a "hodgepodge" of symbols used in different models of heating equipment, some codes for certain devices may be "invisible".

Display The code Decryption
F.00 No signal from supply line temperature sensor.
F.01 No signal from return temperature sensor.
F.02 No signal from the hot water temperature sensor.
F.03 No signal from tank temperature sensor.
F.05 No signal from the external flue gas temperature sensor.
F.06 No signal from internal flue gas temperature sensor.
F.10 Short circuit of the supply line temperature sensor.
F.11 Short circuit of the return temperature sensor.
F.12 Short circuit of the hot water temperature sensor.
F.13 Short circuit of the tank temperature sensor.
F.15 Short circuit of the external flue gas temperature sensor.
F.16 Short circuit of the internal flue gas temperature sensor.
F.20 Temperature limiter triggered.
One of the sensors (in the direct or return line) recorded an excess of the permissible coolant temperature. The causes of the malfunction may be a malfunction of the sensors and the ignition electrode, or insufficiently fast water circulation through the circuit.
F.22 Insufficient amount of water.
The water pressure in the system is below normal. The error appears due to a malfunction of the sensor or circulation pump, as well as due to leaks. In most cases, the problem can be solved by adding water to the system.
F.23 Too much temperature difference.
There is a big difference in the readings of temperature sensors installed on the direct and return lines. It means that the water in the circuit is moving too slowly. The error may mean that the pump is defective or incorrectly configured.
F.24 Temperature rise too fast.
An error occurs if the temperature in the heating circuit rises faster than normal. The malfunction may be due to the fact that the pump does not function or does not work well. Sometimes the cause is a defective check valve.
F.26 Faulty gas fittings.
The gas pressure regulator (solenoid gas valve) does not work due to broken wires, lack of contact at the terminals, damage to the coil, or for other reasons.
F.27 A flame is detected when the gas is off.
The device can "see" the flame when the gas is shut off, if the solenoid valve is damaged and leaky, the ionization electrode is faulty, or water has got on the electronic board.
F.28 The flame was not detected.
The boiler fails to ignite the flame. The error may be due to problems with the gas (if the tap is closed, the gas valve is faulty or the pressure in the line is below normal), air enters the system, malfunctions of the gas fittings, and can also be the result of malfunctions in the ignition system or electronic control unit.
F.29 The flame went out.
The burner goes out during boiler operation due to fluctuations in gas pressure in the line, a clogged flue gas system or problems with internal wiring, ignition electrode, transformer or electronics.
F.32 The fan is running too fast or too slow.
The fan speed is out of range. It may be blocked or defective.
F.33 Pressure switch error.
The causes of malfunctions are usually relay and fan malfunctions. Sometimes the error appears due to damage to the cables, as well as malfunctions of the electronics or the Hall sensor.
F.35 Lack of air.
The boiler does not receive the required amount of air due to a malfunction of the fan or a break in its wires. There may be problems with supply and exhaust air ducts. The signal can be erroneous (due to a malfunction of the Hall sensor or electronics).
F.36 Flue gas leakage.
This error is caused by malfunctions in the air supply and flue gas exhaust systems. All air ducts and chimneys, as well as fans with their cables, are subject to inspection.
F.37 The fan is in emergency mode.
Due to problems with the air supply or due to a clogged smoke exhaust system, the fan runs at an increased speed.
F.42 Coding resistor error.
The resistors that code the boiler power and the type of gas fuel are damaged or missing. It is necessary to check the corresponding section of the electronic board. The error often appears paired with the F.70.
F.45 - F.48 Lack of signals or short circuit of hot water sensors.
F.49 eBUS bus error.
Due to a broken wire, short circuit or overload, the voltage at the eBUS terminals is out of range.
F.50 Flue gas pressure sensor error.
The flue system is clogged or damaged.
F.51 Flue gas leakage is possible.
The sensor indicates that the flue gas temperature is above normal. Possible leak. It is necessary to check the chimney and ensure free flow of fresh air to the boiler.
F.52 No signal from mass flow sensor.
F.53 Mass flow sensor error.
The error appears if the gas pressure is below normal or the filter in the Venturi is clogged with dirt or filled with water.
F.61 Gas valve drive failure.
The shut-off valve is not working properly due to a short circuit, broken wires or electronics faults.
F.62 No connection to gas valve.
There was a delay in switching off the gas valve due to a malfunction of the actuator, a broken cable or a defect in the electronic board.
F.63 EEPROM error.
The electronic board of the control unit is defective.
F.64 Electronics or thermistor error.
Short circuit of the thermistor on one of the circuits or electronics failure.
F.65 Electronics overheating.
The electronic board is too hot due to its own malfunctions or external heating (for example, when the boiler is placed too close to the switched on gas stove).
F.67 Invalid flame signal.
An unrealistic signal from the ionization sensor is recognized, there may be a malfunction in the electronic control unit.
F.68 The flame is unstable.
Unable to ensure stable combustion. The reasons may be air entering the gas pipeline, low gas pressure, clogging of the flue gas system or broken wires in the ignition system.
F.70 Invalid device code.
The boiler setting (during commissioning or after replacing the electronic board) is incorrect.
F.71 Error temperature sensor in the supply line.
F.72 Temperature sensor error in the flow and (or) return line.
F.73 - F.74 Water sensor errors (no signals, short circuits or implausible signals).
F.75 Pressure sensor error when turning on the pump.
F.77 Faulty flue gas valve or condensate pump.
F.80 ActoSTOR sensor error.
F.81 Pump error.
F.83 - F.85 Errors, implausible values or incorrect installation of temperature sensors installed on the pipes of the supply and return circuits.
F.86 Operation of thermal protection in the floor heating circuit.
F.90 No communication with storage module.
F.91 Sensor error on drive module.

This list is not exhaustive. It does not include codes for particularly rare errors, as well as malfunctions that appear exclusively when the boiler is operated in tandem with any specific equipment, such as a solar collector or heat pump.

Control panel of one of the previous generations of Vaillant ecoTEC plus boilers.

Error codes of the most modern Vaillant boilers

The newest (as of 2022) generation of Vaillant gas boilers is equipped with larger displays capable of displaying more characters and more modern control units. The electronic "brains" of these devices can analyze more information and process data from a much larger number of sensors in order to ensure the most accurate operation of the boiler and maximum efficiency. Therefore, the diagnostic system for Vaillant boilers of the latest generation is more complicated than that of the previous ones. It uses a modified error coding system. Codes now consist of the letter F and three numbers.

Boiler control panel Vaillant ecoTEC pro.

This table is a compilation of error codes that appear on the displays of Vaillant ecoTEC plus single-circuit and double-circuit condensing wall-mounted boilers manufactured from 2021. Some codes are accompanied by brief explanations or troubleshooting algorithms. If they are not listed, then problems should be sought in the operation of sensors, plugs or cables.

Display The code Decryption
F.000 No signal from supply line temperature sensor.
F.001 No signal from return temperature sensor.
F.002 No signal from the hot water temperature sensor.
F.003 No signal from tank temperature sensor.
F.010 Short circuit of the supply line temperature sensor.
F.011 Short circuit of the return temperature sensor.
F.012 Short circuit of the hot water temperature sensor.
F.013 Short circuit of the tank temperature sensor.
F.020 Temperature limiter triggered.
The limiter closed the gas valve due to overheating of the coolant in the supply line or return circuit. The error may be due to a malfunction of the sensor, but more often it occurs due to the fact that the circulation pump is blocked or is operating at a capacity below the required one.
F.022 The water pressure is below normal.
The pressure sensor has detected a drop in water pressure below the allowable limit. It is necessary to make sure that there are no leaks and that the sensor is in good condition, and then add water to the system.
F.023 Too much temperature difference.
Excessively large difference between the sensor readings in the supply and return circuits. The error occurs when the pump is defective or is running at reduced capacity due to contamination.
F.024 Temperature rise too fast.
The temperature in the heating circuit rises faster than it should. The appearance of this error code usually means that the pump is not working well or is not configured correctly.
F.025 The flue gas temperature is above normal.
Error reporting overheating in the smoke exhaust system. Most often, it appears if the boiler is incorrectly configured (for example, it runs on propane, but it is set to work on household gas). The reasons for overheating can also be incorrect installation (too close to the gas stove) or excessive boiler power for this heating circuit.
F.027 The burner is off but a flame is detected.
The ionization sensor "sees" the flame, despite the shut off gas and the burner off. Problems may lie in a malfunction of the sensor itself, malfunctions of the gas fittings (for example, the valve passes gas) or moisture on the electronic board.
F.028 The flame is not detected.
Cannot ignite burner. This problem can have many causes: blocked gas or low gas pressure in the line, malfunctions of the relay or solenoid valve, blocking the air supply or clogging of the flue gas removal system, breaks in the ignition circuit or electronics malfunctions.
F.029 The flame went out.
The burner went out, the re-ignition failed. The error may be a problem with the gas supply, a malfunction of the electrode or transformer, a clogged condensate drain pipe, or a blockage in the chimney.
F.032 The fan rotates too slowly.
The fan speed may be slow if it is blocked by dirt particles or foreign objects. When the fan stops completely, problems may be poor contacts on the plug, damage to the power cable, a malfunction of the Hall sensor, or a defect in the electronic board.
F.035 Blocking the air supply or flue gas outlet.
The boiler is unable to maintain normal operation due to lack of fresh air. Either the air does not enter the furnace in the proper volume, or the flue gases do not leave the combustion chamber. A complete check of both systems is required, as well as the electrodes with their cables and the condensate drain pipes.
F.040 Excess air ratio below normal.
The boiler fails to maintain the optimal ratio of air and gas fuel. It is necessary to check the boiler settings, the condition of the gas fittings and the flue gas exhaust system, the operation of the fan and the gas pressure in the line. Sometimes this error appears due to a clogged condensate drain pipe.
F.042 Coding resistor error.
Boiler settings set with coding resistors are incorrect or not readable. You should check the control board and the wiring harness leading to it.
F.044 Incorrect control electrode ionization signal.
The error is caused by: electrode malfunctions or wire breaks, electronics or gas fittings malfunctions, blockages in the chimney or condensate drain pipe, as well as problems with pressure or gas quality.
F.047 Invalid temperature sensor signal at the outlet of the internal tank.
F.049 eBUS bus error.
Due to damage, overload, incorrect installation or power surges in the network, the operation of the eBUS bus is disrupted.
F.057 Failure in combustion control.
The boiler has malfunctioned. Causes can be: blockage of the flue path, defective gas valve, blockage in the condensate siphon, damage to the fan or problems with the electronics.
F.061 Gas valve drive failure.
There are delays or failures in the control of the gas valve. Malfunctions may lie in the valve itself, as well as be the result of a short circuit or a malfunction of the electronic boiler control unit.
F.062 Problems with turning off the flame.
The error may appear due to a malfunction of the gas valve, electronic board or ignition electrode.
F.063 EEPROM error.
The board is defective and needs to be replaced.
F.064 The signal cannot be interpreted.
It is not possible to receive or process a signal from one of the temperature sensors (on the supply line or in the return circuit). The reason may be a malfunction of the sensor or problems associated with the boiler electronics.
F.065 Electronics overheating.
The temperature of the electronic board is critically high. The error may be the result of a malfunction of the control board or a consequence of external heating.
F.067 Malfunction of the ionization sensor.
The flame control system indicates a problem. They may be a malfunction of the electrode, cables or control electronics. Sometimes this error appears due to incorrect operation of the flue gas exhaust system.
F.068 Unstable flame.
The burner is unstable. The reasons may lie in gas pressure surges, a faulty gas valve, the presence of air in the gas pipeline, an incorrect air to gas ratio, a malfunction of the control electrode. This problem also manifests itself if the chimney is blocked or the condensate drain pipe is clogged.
F.070 Invalid device code.
The boiler is configured incorrectly, an incorrect power value of the device is “flashed” in the control unit. Reconfiguration required.
F.071 Supply line temperature sensor error.
F.072 Incorrect difference between the temperature sensors in the supply line and the return circuit.
F.073 Short circuit of the water pressure sensor.
F.074 No signal from water pressure sensor.
F.075 Pressure sensor error when starting the pump.
F.076 Primary heat exchanger fuse defective.
F.077 External equipment error (flue gas valve or condensate pump).
F.078 The external temperature controller is not compatible with this boiler.
F.080 Error in the cold water temperature sensor at the inlet to the storage tank.
F.081 Failure to fill the storage tank with water.
This error can be caused by a pump malfunction or blockage, wire breakage, three-way valve inoperability, or deposits on the secondary heat exchanger.
F.083 Slow heating.
The electronics detects a too slow rise in temperature if the pressure in the system is below normal or the temperature sensors are faulty.
F.084 Temperature sensors in the supply and return circuits are installed incorrectly or are interchanged.
F.085
F.087 No connection to ignition transformer.
F.088 No connection to solenoid gas valve.
F.089 The pump is connected incorrectly or is not compatible with this boiler.
F.090 No connection to internal storage.
F.092 The conversion of the boiler to work on a different type of gas was not carried out correctly.
F.095 Gas valve actuator malfunctions.
F.096
F.194 The electronic board power supply is defective.
F.195 The voltage in the network is much lower than normal.
F.196 The voltage in the network is much higher than normal.
F.317 Error of the volume flow sensor of water in the hot water circuit.
F.318 Malfunction of the three-way valve actuator.
F.320 The heating pump is blocked, attempts to unlock it failed.
F.321 The pump electronics are faulty.
F.322 Overheating of the heating pump.
F.323 The heating pump runs dry.
F.324 The heating pump is not powered.
F.325 Blockage or malfunction of the heating pump.
F.326 Hydraulic sensor or actuator error.
F.344 The control electrodes must be replaced.
F.346 Difficult ignition.
The electronics have determined that the burner is igniting with considerable difficulty. Almost all components and assemblies of the boiler are subject to verification
F.707 There is no communication between the display and the electronic control unit.
F.905 The communication interface is not working.

This table does not list all error codes that cause failures in the operation of Vaillant boilers, but only a part of them. A full version of the table describing all possible malfunctions and malfunctions can be found in the "Installation and Service Manual" for a particular model of equipment.

What to do if the Vaillant boiler constantly knocks out errors

Vaillant heating equipment is considered to be of high quality and reliable. But it is not immune from errors and malfunctions. In the boiler manuals, the manufacturer strongly advises users not to interfere with the operation of the equipment (except for basic settings and adjustments, as well as adding water to the system). In all other cases, it is recommended to call the service center that maintains boilers of this brand and call a specialist. Therefore, this article should be considered solely as a source of information about malfunctions in Vaillant boilers, and not as a repair guide.

However, owners of heating equipment have the opportunity to significantly reduce the number of error messages. To do this, you need to connect the boiler not directly to the network, but through a stabilizer or UPS. Electronic modules that control the operation of boilers, and sensors that record the main operating parameters, are very sensitive to voltage surges and drops. A stabilizer or uninterruptible power supply can provide more "comfortable" conditions for the operation of heating equipment.