Vaillant Boiler Problems, Service & Repairs


The Vaillant fault and looking for a cure before it comes too much of a problem or require an engineer for an emergency boiler repair.


Vaillant Boiler Problems, Service & Repairs


Below we’ve created a detailed guide to Vaillant boiler problems, and what you need to do next in terms of servicing and repairs of which you can click on to read a complete article about the code in question or you could continue just reading the paragraphs further below.

When a Vaillant boiler becomes faulty, a fault code will be shown on the display panel. Typical examples of a fault code include F20, F29 and F75.

To diagnose the fault and understand the potential fix, you’ll first need to determine what fault code your boiler is displaying.

Once you’ve done this, you’ll be able to highlight the issue below, then click through to the relevant guide that explains the problem further.

The guide below is in alphanumeric order with F20 being first, and F89 being last.

Vaillant Boiler Fault Codes Problems And Cures

My Vaillant boiler is displaying the F20 fault code, what does this mean?


The F20 Vaillant boiler fault code signifies a problem with the boiler overheating.

Your boiler has devices called NTC thermistors fitted. They monitor the water temperature out of your boiler (the flow) and into the boiler (the return). If these temperatures are too high, it will lockout due to overheat.

This fault is commonly caused by low boiler pressure. When boiler pressure is low, that’s a sign of lack of water in the system.

This can create a dry fire scenario, which could fry internal boiler components.

My Vaillant boiler is displaying the F22 fault code, what does this mean?


The F22 fault code is caused by low water pressure in the system.

When an engineer sees the F22 fault code they are going to be looking for:

  • Leaks coming from the boiler’s internal components (for example, the heating pump)
  • Leaks in the central heating system (for instance, a weak copper joint)
  • Faulty expansion vessel or pressure release valve

My Vaillant boiler is displaying the F23 fault code, what does this mean?


Like many fault codes, the F23 isn’t particularly specific in terms of diagnosing the boiler part that’s at fault.

However, it does highlight the issue; the differential between flow and return pipe temperatures is too high.

There should be a slight differential in temperature. Hot water leaves the boiler (flow) and then is cooled as radiators and towel rails absorb some of its heat. It then returns to be reheated by the boiler (return).

However, the boiler recognises if there’s a big temperature differential being caused by faults.

These faults can come from:

  • Faulty heating pumps
  • Airlocks in the boiler or heating system
  • Faulty NTC thermistors
  • A problem with the heat exchanger

My Vaillant boiler is displaying the F24 fault code, what does this mean?


For boiler components to do their job, there needs to be sufficient circulation. In the case of the Vaillant boiler F24 fault code, the water circulation is either non-existent or at least, not sufficient.

The causes of a water circulation fault usually lie with the pump. If the pump is partially seized or is set to the wrong flow speed, it won’t provide the power the heating system needs.

However, a boiler engineer will also check for other issues that could contribute to the water circulation fault including:

  • Isolation valves set in the closed position
  • A blocked heat exchanger
  • Air locks

My Vaillant boiler is displaying the F27 fault code, what does this mean?


If there’s a problem with your boiler producing or maintaining a flame, it’s likely to show the Vaillant boiler F27 fault code.

This fault code is usually displayed if there is:

  • Excess moisture on the electrics
  • The ignition leads or electrode need replacing
  • The PCB is malfunctioning and either needs to be repaired or replaced

However, the problem here might not be the flame at all.

Your boiler engineer will have to inspect every component relevant to a flame, and that includes the flame sensor. If the flame sensor is faulty, it might assume there isn’t a flame, even when there is.

My Vaillant boiler is displaying the F28 fault code, what does this mean?


The Vaillant boiler F28 fault code is a hard one to fix, because the list of potential faults is long.

The F28 code refers to anything that could stop the boiler from igniting. However, the most common cause of the F28 fault code showing is going to be a gas supply or air pressure related fault.

On the gas side, your boiler engineer will be checking things such as:

  • Gas supply to meter
  • The gas meter regulator isn’t frozen or blocked
  • Pre-paid meters have been topped up and reset correctly
  • The gas valve is correctly adjusted, and not faulty (i.e. it moves freely)

However, if it’s likely to be an air circulation fault, they’ll need to test for things such as:

  • Flue blockages
  • Air pressure switch faults

My Vaillant boiler is displaying the F29 fault code, what does this mean?


The Vaillant boiler F29 fault code refers to a flame failure during operation. This isn’t to be confused with other fault codes where the flame fails to ignite.

Here we’d be looking for problems such as:

  • A gas supply issue for example, the gas valve is incorrectly adjusted and not providing the boiler with enough gas
  • Gas valves that are sticking or not opening correctly
  • The jet on your boiler is blocked with debris, and limiting the flow of gas to establish a solid flame
  • A problem with the flue

As most of the potential faults here relate to electronic components, the PCB (printed circuit board) will need to be tested too.

My Vaillant boiler is displaying the F32 fault code, what does this mean?


If your Vaillant is showing the F32 boiler fault code, your issue is an air fault.

In boilers there are two main culprits for air faults:

  • The fan
  • The flue

First, a quick visual inspection will ensure the flue isn’t blocked.

Typically, we find the fan is usually to blame. It could be a minor issue such as the fan’s rotation speed isn’t correct. However, old fans can deteriorate quickly.

And, as this component is designed to help expel dangerous flue gases from your property, it will need to be replaced as soon as possible if it’s at fault.

My Vaillant boiler is displaying the F61 fault code, what does this mean?


The F61 Vaillant fault code refers to a faulty gas valve. This shouldn’t be confused with an incorrectly adjusted (but still operational) gas valve.

Without a working gas valve, your boiler won’t be supplied with enough gas, and won’t produce sufficient heat.

A gas engineer will be able to determine if the gas valve is at fault and replace it if necessary.

My Vaillant boiler is displaying the F62 fault code, what does this mean?


The Vaillant F61 fault code will be displayed if there’s a flame detected after the gas valve is closed. As this is a gas safety issue, it needs to be looked at by a Gas Safe engineer as soon as possible.

Although it could be linked to a gas valve fault (like the F61 fault code), it could also be an electrical malfunction.

My Vaillant boiler is displaying the F63 fault code, what does this mean?


The Vaillant boiler F63 fault refers to a PCB not working correctly. The potential causes include:

  • A faulty PCB that is giving or receiving the wrong signals
  • Loose or damaged connections to the PCB
  • The PCB has not been setup correctly by a service engineer

Using a multi-meter, a Gas engineer will be able to determine which of the three issues above are causing the problem.

My Vaillant boiler is displaying the F64 fault code, what does this mean?


The F64 Vaillant boiler fault code will occur when there’s a rapid change in temperature from the NTC thermistors. These components monitor water temperature on the flow and return.

This issue could be caused by:

  • Faulty NTC thermistors
  • Limescale build-up on the NTC thermistors that is causing hotspots
  • An electrical issue causing the wrong signals to be sent to the PCB

My Vaillant boiler is displaying the F65 fault code, what does this mean?


A Vaillant F65 fault code can be related to damaged connections on a PCB, meaning the boiler will work intermittently.

However, it’s more likely that it’s a mains voltage problem.

Overvoltage can fry electrical boiler components. So, whilst the PCB needs to be tested first, it’s worth checking all electrical components for damage.

My Vaillant boiler is displaying the F67 fault code, what does this mean?


Your boiler will lockout and display the F67 Vaillant fault code if it doesn’t recognise a flame, which is the case here.

Typically, this is an electrical issue related to the PCB. Faulty connections and wiring will need to be repaired or replaced.

After assessing damage to the PCB, the next step is to check the flame sensor.

Just because the PCB thinks there’s no flame, doesn’t mean that’s the case. If the flame sensor is faulty, this could be a quick and easy fix with a replacement.

My Vaillant boiler is displaying the F68 fault code, what does this mean?


The F68 Vaillant fault code relates to a fluctuation in flame signal. So, the boiler is producing a flame, but it’s weak or keeps going out.

This could be due to:

  • A blockage in the flue
  • The air pressure switch being faulty
  • A faulty fan
  • Incorrectly adjusted gas valve
  • Debris in the burner

My Vaillant boiler is displaying the F70 fault code, what does this mean?


The F70 Vaillant fault code relates to a software problem. Typically, we find this is a problem when a new PCB has been fitted, but not correctly setup by the engineer.

However, if your boiler is old, it could be faulty software. The fix is a replacement PCB, as software problems on older boilers are rarely an easy fix.

My Vaillant boiler is displaying the F71 fault code, what does this mean?


The F71 Vaillant fault code relates to a boiler with no flow (water out of your boiler) temperature change when it fires up.

This could be due to an NTC flow thermistor that’s not been installed correctly or faulty, or even a broken heat exchanger.

My Vaillant boiler is displaying the F72 fault code, what does this mean?


The F72 Vaillant fault code will show when there’s a permanent temperature difference between the flow and return NTC thermistors.

Your Gas engineer will need to determine if this is due to the wiring, incorrect installation (the NTC thermistors have been fitted on the wrong pipes), or faulty NTC thermistors.

My Vaillant boiler is displaying the F73/F74 fault code, what does this mean?


This is a low-pressure water sensor fault. The boiler may think that water pressure is low, even though it’s not (because the sensor is faulty).

Sensors are not particularly expensive to replace, so this should be a cheap fix.

My Vaillant boiler is displaying the F75 fault code, what does this mean?


The F75 Vaillant fault code can be due to similar faults listed for F73/F74.

However, we find on most occasions the F75 relates to a pump that’s not running, rather than faulty low-pressure water sensor.

My Vaillant boiler is displaying the F83 fault code, what does this mean?


The F83 problem can stem from many issues including:

  • A fault in the wiring between the PCB and the NTC thermistors
  • A blocked or cracked heat exchanger
  • Low water pressure causing a dry fire

My Vaillant boiler is displaying the F84 fault code, what does this mean?


The F84 Vaillant fault code occurs when the boiler notices a permanent temperature difference between the NTC thermistors, much like the F72 fault code.

Although faulty NTC thermistors can be blamed, it’s likely your boiler engineer is going to be testing the wiring harness. Over time, these can degrade and cause communication errors with the PCB.

My Vaillant boiler is displaying the F85 fault code, what does this mean?


This is rarely a major issue. Like the F84 Vaillant fault code, it relates to an NTC thermistor problem.

They’re likely faulty or fitted to the same pipes. So, they’ll need to be installed correctly, or replaced.

My Vaillant boiler is displaying the F88 fault code, what does this mean?


The F88 Vaillant fault code is one of the more specific codes. It relates not just to the gas valve, but it’s electronics.

Typically, these faults occur due to old age or water damage. Where water damage is the issue, the valve needs to be replaced and the leak found and fixed.

My Vaillant boiler is displaying the F89 fault code, what does this mean?


This is an electronic pump fault. The wiring to or from the pump is defective and needs to be repaired or replaced.

A heating engineer will be able to determine exactly where the fault lies by using a multi-meter.

Other boiler issues relating to other manufactures


For more boiler issues then please visit the Boiler Problems And Cures page.