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Last updated: 9th April, 2024


Vaillant F24 Error Code - How To Fix

Vaillant F24 Error Code - How To Fix

Key takeaways

  • The Vaillant F24 error code can be caused by several things, including: faulty pump, isolation valves, airlocks and faulty electrics.
  • If the problem is with your boiler's airlocks, opening the valves may fix the problem.
  • If the boiler issue is with its PCB, you'll need a Gas Safe registered engineer.

Any time a boiler error code presents itself it can be anxiety and stress inducing, but fear not, at iHeat we want you to be as informed as possible.

In this blog we’ll be taking a look at the Vaillant F24 error code including its meaning as well as its causes, and how it can be fixed.

What is an Error code?

An error (fault) code is an alphanumeric code displayed when a boiler isn’t functioning as it should. The code booth alerts the owner something is wrong and informs them of the type of issue occurring.

By identifying the specific error code, homeowners and heating engineers can quickly diagnose the issue and take the appropriate steps to fix it.

Vaillant 24 Error Code

The F24 error code displayed by Vaillant boiler models is an indication that the water is not flowing properly through the pipework of your heating system. 

When this occurs, the boiler will lockout or shut down as a safety measure and to protect its functionality, while displaying the F24 code.

As water is a crucial component in a heating system, it is responsible for heating up the radiators and providing hot water for various uses, such as showering. Therefore, the F24 fault code suggests that there is either no water flowing through the heating system or very little water flow. 

This issue can lead to a malfunctioning heating system, preventing it from providing heat and hot water to your home.


There are several potential reasons why there may be a lack of water circulation in your heating system, leading to the F24 error code:

Faulty Pump 

One of the most common reasons for this issue is a faulty pump. Blockages are often caused by debris in the pump, leading to a cease in operation or seized components, incorrect speed settings, or other reasons that may cause pump components to falter.

Isolation Valves

If your boiler was recently serviced, it's possible that if carried out by a non professional the isolation valves were mistakenly left in a closed position. This can obviously prevent water from circulating as it should, resulting in the F24 error code.


The presence of trapped air (airlocks) in the heating system can slow or even stop water flow, leading to the F24 code.

Faulty Electrics

A less frequent cause of the F24 fault is if there is an issue with the wiring that connects the pump and PCB. This may be a false flag as an F24 error code may be displayed without any water flow problems actually happening.

How to Fix

Resolving a Vaillant F24 error code depends on the cause of the issue.

If the error was caused by closed isolation valves, simply opening the valves should fix the problem. 

However, if the issue is with the PCB, it may need to be replaced, which can be costly, around £510. In such cases, it may be more cost-effective to replace the boiler entirely with a new model.

Airlocks can be resolved by applying pressure to the affected areas, such as the pump, radiators, or towel rails in your home. A professional can inspect and offer advice on cleaning or replacing damaged parts.

While fixing the isolation valves is a task that can be accomplished by homeowners, other issues may require professional assistance. For example, if the pump has become stuck due to debris, a professional should be contacted.

If you suspect an airlock is causing the issue, you can attempt to manually bleed it. To do this, close the gate valves to stop water from entering, then slowly loosen the bleed screw. 

As the air escapes, it will produce a hissing sound and be replaced by a small amount of liquid water. Open the gate valves at the ends of your boiler and restore water flow and flush all radiators as a precautionary measure.



Arranging for your boiler to be annually checked over or ‘serviced’ by a qualified engineer can be a fantastic way of analysing the state of your heating system in yearly increments, identifying and rectifying any faults before they have a chance to progress.

Boiler Upgrade

While an individual component such as a pump or sensor can be replaced in isolation, if your boiler is starting to show signs of more serious or repeat decay, it may be beneficial to upgrade to a newer, more efficient boiler.

Be Proactive With iHeat

The best way of ensuring your boiler is operating as it should, is by proactively replacing ageing or faulty boilers at the earliest signs of degradation, this preventative step is far more prudent than reactive maintenance.

It’s a mechanical and engineering fact that due to some of the technological advancements in recent times, modern boilers are more robust and efficient than anything made previously. 

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Frequently Asked Questions

How Do I Fix Error Code F24 on a Vaillant Boiler?

Error code F24 on a Vaillant boiler indicates a system temperature rise too fast, possibly due to low water content, a circulation problem, or a scale build-up in the heat exchanger. To fix this, you might need to check and ensure the system is properly filled with water, bleed radiators to remove any air trapped in the system, and ensure the pump is functioning correctly. If the problem persists, it might be necessary to call a qualified heating engineer to inspect and possibly descale the heat exchanger or address any other underlying issues.

What is the Fault Code 24 on a Boiler?

Fault code 24 on a boiler can vary in meaning depending on the brand and model. For Vaillant boilers, as mentioned, it typically refers to a system temperature rise too fast, suggesting issues with water circulation or volume. It's essential to consult the specific boiler's manual or contact a professional for the exact interpretation and recommended actions based on the brand.

Why is My Glow Worm Boiler Flashing F24?

On a Glow Worm boiler, flashing F24 similarly indicates a problem related to water circulation or a rapid temperature rise within the system. This could be due to low water pressure, a faulty pump, or a blockage in the system preventing proper water flow. Checking the water pressure and ensuring the system is correctly filled, along with bleeding any air from the radiators, can be initial steps to troubleshoot this issue.

How Do I Fix F22 on My Vaillant Boiler?

F22 is a common fault code on Vaillant boilers indicating low water pressure. To fix this, you need to repressurize the system to the recommended level, usually around 1.0 to 1.5 bar. This can be done by opening the filling loop valves beneath the boiler until the pressure gauge reaches the correct level, then securely closing the valves. If the pressure drops again shortly after, this may indicate a leak in the system, requiring professional assistance.

What Does F24 Mean on a Vaillant Boiler?

As previously mentioned, F24 on a Vaillant boiler signifies a rapid rise in system temperature, which can be due to issues like low water content, poor circulation, or a scale build-up in the heat exchanger. Addressing this involves checking water pressure, ensuring proper circulation, and potentially seeking professional help for more complex issues like descaling the heat exchanger.

Why is My Vaillant Boiler Losing Pressure F22?

The F22 fault code on a Vaillant boiler indicates low system pressure, which can happen due to several reasons such as leaks in the system, recently bled radiators, or a need for repressurization after maintenance work. Identifying and fixing leaks, repressurizing the system, and ensuring it's correctly filled can resolve this issue.

How Do I Get the Pressure Back Up on My Vaillant Boiler?

To increase the pressure in your Vaillant boiler, locate the filling loop (usually underneath the boiler) and slowly open the valves to allow water into the system. Watch the pressure gauge, and once it reaches the recommended level (around 1.0 to 1.5 bar), close the valves. If you're unsure or if repressurizing does not solve the issue, it's best to consult a professional heating engineer.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.