Vaillant Boilers Problems: 8 common problems and their solutions


It’s important to know the problems and effective solutions for the Vaillant boiler. Vaillant boilers (closely related to Saunier Duval boilers) are among the most installed boilers of all time. This is due to their high output, superb performance, low consumption, intelligent and user-friendly interface, and the highest ratings for low NOx, reduced pollutant emissions and ability to work in conjunction with solar installations.

But no boiler, however efficient it may be, is exempt from having malfunctions, or even breakdowns at some point in time. Fortunately Vaillant boilers incorporate an effective system of error codes, specialized and accurate, which helps to detect faults well and guides on possible solutions. In this article we will talk in detail about 8 of the most frequent Vaillant boiler problems and how to solve them. All the content will be supported by helpful illustrations and tables.

In this article we will be taking the Vaillant EcoTEC boiler model as a reference. Here you can find the link to download the manual for this boiler from the official manufacturer. However, this does not mean that this tutorial is not applicable to other Vaillant models, even older models (such as the Vaillant AtmoTEC). The error codes are not always exactly the same, but in general the faults are the same, and so are the solutions.


Vaillant Boiler: The 8 most common problems (table)

In the table below we have put together, rather than 8 error codes, 8 groups of error codes more or less related to the same area of the boiler. Following the table we will go into more detail about these Vaillant boiler errors, and break down the specifics of the codes in each of the groups.

Vaillant Boiler: The 8 most common problems
F0 to F11Failure in the temperature probes.Check if the flow and return probes are broken or short circuited and fix them.
F22 | F23 | F24Lack of water.Refill the system. Check the pressure sensor and circulation pump.
F27 | F28 | F29Lack of gas.Check and restore gas supply and installation and ignition circuit.
F32 | F37 | F38Malfunctioning fan.Plugging, checking or unclogging fan.
F61 | F62Gas valve failure.Check gas fittings and circuit board.
F63 a F67Malfunctioning electronic components.Check if the circuit is faulty, short circuited, or excessively hot.
F71 | F72Fallo en las sondas de temperatura.Verificar si las sondas están mal colocadas o averiadas y repararlas o reemplazarlas.
F75Fallo en la bomba de circulación.Desatascar o reemplazar la bomba de circulación.

F0 to F11: Failure in the temperature probes

In general, error codes between F0 and F11 refer to different failures in the inlet and return temperature probe, either by interruption or short-circuit.

Vaillant boiler problems
F0Input temperature probe interruption. NTC connector loose or not inserted; PCB multi-connector incorrectly plugged in; interruption in the wiring harness; faulty NTC
F1Interruption of the return temperature probe. Return. NTC connector loose or not inserted; PCB multiple connector incorrectly plugged in; interruption in the wiring harness; faulty NTC.
F10Short circuit in faulty NTC input temperature sensor; short circuit in wiring harness, cable/casing.
F11Short circuit in return temperature sensor. NTC faulty; short circuit in wiring harness, cable/casing.

F22 | F23 | F24: Falta de agua

Lack of water is a generic problem for any boiler, including Vaillant boilers. The lack of water may result from several factors, from leaks in the boiler or installations, to faulty, incorrectly opened or closed filling, draining or safety valves, or problems with the circulation pump.

Similarly, lack of water can appear problematic in several different ways, from a drop in pressure in the heating system to overheating due to insufficient water flow. The generic solution for this issue is to restore the water level by opening the filler tap, repairing leaks or unclogging the water circulation pump.

Vaillant boiler problems
F22Safety lockout due to lack of water. There is little or no water in the unit. Water pressure sensor may be faulty. The cable to the pump or water pressure sensor may be loose, disconnected or faulty.
F23Safety lockout due to excessive temperature variation. The circulation pump is blocked or has reduced power. Air has leaked into the unit. Inlet and return NTC interchanged.
F24Safety lockout due to too high a temperature rise. The circulation pump is blocked or has reduced power. Air has leaked into the unit. Insufficient pressure in the system. Gravity brake blocked or incorrectly mounted.

F27 | F28 | F29: Lack of gas

This section concerns only Vaillant gas boilers with problems. Vaillant diesel boilers have nothing to do with this fault, of course. There are several reasons why a boiler may have a lack of gas, and all of them will block the equipment until the fault is repaired and the fuel supply is restored. Some of the error codes associated with lack of gas are:

Vaillant boiler problems
F27Safety lockout due to flame simulation. The electronics are wet, the electronic flame control is faulty, or the gas solenoid valve is not sealed.
F28There was a start-up failure. The gas meter is malfunctioning. The gas pressure control is activated. The gas has air in it. Gas flow has insufficient pressure. Thermal locking device (TAE). Condensate line is blocked. Gas nozzle is incorrect. Gas fitting is malfunctioning. The printed circuit board multiple connector is incorrectly plugged in. Fault in any component of the ignition system (transformer, cable, connector or connection electrode). Ionization current (cable, electrode) is interrupted. There was a fault in the grounding of the device or in the electronics.
F29Too many unsuccessful ignition attempts. Gas supply has been interrupted. You should check the exhaust gas recirculation in the condensing boiler. The condensate pipe is clogged. Incorrect grounding. Ignition failure in the ignition transformer.

F32 | F37 | F38: Cooling fan failure in condensing boilers

The Vaillant condensing boiler can also experience issues, and a common one in the Vaillant EcoTEC boiler in this regard is that the fan gets stuck or breaks down. This will of course generate problems of excess temperature and inability to expel the combustion fumes, so the boiler will automatically block until this is resolved.

The Vaillant Ecotec Plus reports this fan failure via code F32, and other models may report it via codes F37 and F38.

Vaillant boiler problems
F32 | F37 | F38A fan failure has occurred. It will be necessary to check if the fan connector is plugged in incorrectly. Check if the multiple connector on the printed circuit board is plugged in incorrectly, or if there has been a break in the wiring harness. The fan may be blocked and may produce over-temperature errors or smoke ejection deficiency. The Hall sensor may be faulty. A malfunction may have occurred in the electronics.

F61 | F62: Malfunction in the gas valve

This type of failure is related to lack of gas, but not in the fuel supply, but with failures in the set of valves that carry the gas from the gas tank to the burner of the boiler. The failure may not be related to the gas itself but to a malfunction in the detection of the flame by the electronic circuit, even if there is actually a flame.

Vaillant boiler problems
F61There is an activation issue with the gas valve. The gas valve fails to activate. The supply line from the wiring harness to the gas valve is defective due to grounding or short-circuit, or the defective gas valve itself may be damaged. The printed circuit board may be defective.
F62There is a delay when disconnecting the gas valve. Delayed shutdown of the gas valve has been detected. External light (ignition and control electrode shows a delayed shutdown of the flame signal). The gas valve is defective. The printed circuit board is defective.

F63 a F67: Electronic components malfunction

Vaillant boiler problems
F63EEPROM error in the electronic components.
F64A malfunction has been detected in the electronics / NTC. The flow or return NTC is short-circuited. A malfunction has occurred in the electronics.
F65A malfunction has been detected in the electronics. The electronics are excessively hot due to an external factor. Some malfunction has occurred in the electronics.
F67A malfunction has been detected in the electronics/flame. The flame signal is not plausible. There is a malfunction in the electronics.

F71 | F72: Temperature sensor malfunction

Vaillant boiler problems
F71There has been a malfunction in the inlet temperature sensor. The inlet temperature sensor registers a constant value. The sensor is incorrectly positioned in the inlet duct. The flow temperature sensor is damaged.
F72A malfunction has occurred in the inlet and return temperature sensors. There is an excessive temperature difference between the inlet and return NTCs. A malfunction has occurred in the inlet temperature sensor and/or the return temperature sensor.

F75: Circulation pump malfunction

A malfunction in the circulating pump causes a water shortage fault. The circulation pump often clogs, but it can be unclogged by the simple method of opening the outer cover of the boiler, locating the pump, removing the peculiar plastic plug covering its shaft and, using a wide-bladed screwdriver or some such tool, gradually turning the pump shaft until it unclogs.

This might now work out, sometimes, and you need to replace the pump.SEE THE CIRCULATION PUMPS AVAILABLE ON SALE FROM SUNER.

Vaillant boiler problems
F75A malfunction has occurred. A pressure change cannot be detected when starting the circulation pump. The water pressure sensor and/or the circulation pump are faulty. Air has leaked into the heating system. The water volume in the unit is not adequate. Check the adjustable bypass valve and connect an external expansion chamber to the return.


Here you will find concise answers to frequently asked questions from users on topics that are in some way related to the subject of this article.

What pressure does a Vaillant boiler have to have?

For a Vaillant boiler to work properly, the filling pressure of the boiler must be between 1 and 2 bar (i.e. between 0.1 MPa and 0.2 MPa), with the heating system cold and full. This applies to a single-storey house. However, if the heating system is located in a multi-storey house, higher filling pressure values may be required. This prevents air from entering the system.

The Vaillant boiler incorporates a water pressure sensor, which will notify the value by flashing on the display whenever the pressure drops below 0.6 bar (0.06 MPa). And if the pressure drops below 0.3 bar (0.03 MPa), the unit locks and the system stops in order to prevent breakage.

How can I increase the pressure?


To increase the pressure in a boiler, the simplest and most direct method is to fill the heating circuit with water. First you have to find the filling valve, open it wide and let the water in until the pressure gauge reads between 1 and 2 bar. When the pressure has already normalized in this way, don’t forget to close the inlet tap, because it could cause excess pressure.

In these cases where the boiler locks up because of excessively low pressure, the display will show an error code F22 (in the case of Vaillant EcoTEC boilers), which will keep flashing until the system is refilled with water and reaches a minimum of 1.1 bar. If water loss is frequent, it might be leaking.

Why won’t the boiler start?

When a boiler won’t ignite, this could be for many possible reasons. For example: failure in the fuel supply (because it ran out or because a valve remained closed), faults, cuts or short circuits in the electrical supply or in the ignition circuit, low pressure due to lack of water, dirty, misaligned or faulty electrodes, dirty burner or injector, fuel pump breakdown or clogged, thermostat failure, dirty or faulty photocell, obstruction in the smoke outlet, clogged or faulty water circulation pump, excess temperature, because the service to be given by the boiler is greater than its capacity, or simply due to lack of general maintenance.

What does an F 28 error mean in a Vaillant boiler?

The F28 error in the Vaillant boiler is a safety control mechanism included in the equipment. In general it’s an ignition failure, but in particular it can be due to several causes, from a cut in the gas supply to an interrupted or short-circuited wiring. The error code F28 in the Vaillant boiler is one of those malfunctions that completely blocks the boiler from working until there is human intervention to fix the problem which caused the ignition failure.

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