The Vaillant F75 Fault Code Error and How To Clear It

Most of the modern boilers are equipped with a self-safety mechanism to protect their internal components from damage. The safety mechanism works automatically, with sensors and other electronic components installed in the modern boilers. When triggered, the boiler's safety system shuts it down and displays the relevant error code.

What an error code refers to may differ depending on the make and model of a boiler, details of which are mostly available in the relevant user manuals. The Vaillant boiler is one of the most popular brands in UK homes, and the "F75" fault code is one of the most common issues Vaillant boiler owners have experienced. When this error code appears on a Vaillant boiler, especially on EcoTech models, homes may experience a lack of heating and no hot water at taps. The obvious reason is that the boiler shut down due to the safety mechanism activating, but it is very important for homeowners to understand what actually happened to the boiler and how to fix it.

Keep reading this blog to understand everything related to the F75 fault code in a Vaillant boiler, what it means, why it happens, and how to clear it.

Understanding What The Vaillant F75 Fault Code Refers To

The fault code F75 on a Vaillant boiler indicates that the boiler is unable to detect a rise in water pressure. While it may also refer to a general fault with the system pressure, more relevantly, it points to a problem where the change in pressure is not being detected by the boiler, especially when its pump starts up.

When the boiler is cold, the normal pressure ranges between 1.0 and 1.5 bars. Once the boiler starts heating the water, the water pump is also turned on to circulate water. The immediate result of turning on the pump is a slight rise in boiler pressure. If everything is working normally, the sensors can sense the rise in pressure. But when, for one reason or another, the boiler fails to detect a rise in pressure, the safety system is activated, forcing the boiler to shut down and displaying fault code F75.

So, the F75 fault code specifically means “the boiler is unable to detect pressure change and has locked out as a safety measure”.

Common Reasons Why the F75 Fault Occurs

There are several possible reasons for the F75 fault code in Vaillant boilers, including a faulty pressure sensor, a faulty pump, or a fault in the central heating system. More importantly, the major cause is often the boiler's inability to detect the change in pressure.

·        System Pressure Is Low

The F75 fault code specifically indicates the boiler's inability to detect a change in system pressure, but it may also appear if the system pressure drops too low. Normal cold pressure of a boiler ranges from 1.0 to 1.5 bars. If, due to any reason, the pressure drops well below the 1.0 bar threshold, typically below 0.5 bar, the F75 code may appear. The reason is that when pressure drops or rises, and the boiler system cannot detect this change due to insufficient water in the system, the F75 fault code will be displayed, shutting down the boiler to protect it from damage.

In this case, the fault code F75 can be easily fixed by topping up the pressure, especially when the pressure drops below 1.0 bar.

·        The Pressure Sensor is Either Blocked or Faulty

A pressure sensor is one of the most sensitive components of a boiler, as it is designed to detect changes in water pressure, whether up or down. It is an important monitoring system, as the central heating system's operation largely depends on correct water pressure.

A fault in a pressure sensor can cause it to stop or produce incorrect pressure readings. The fault might be due to an electronic failure, a blockage caused by limescale build-up, or debris accumulation around it.

When the sensor fails to detect pressure or detects it incorrectly, especially when the pump is started, and pressure starts rising but is not detected by the pressure sensor, the boiler shuts down, giving the F75 error code. This is one of the most common reasons for the F75 fault code.

·        The Pump is Not Working or Fails Due to An Airlock

A pump circulates hot water throughout the central heating system. But sometimes it fails to do this job due to one reason or another. It may have developed an internal fault, be blocked or seized, or have stopped working due to an airlock. When it happens, the boiler fails to circulate hot water properly. As a result, the pressure sensor does not detect a rise in water pressure, which triggers the safety mechanism, and the boiler shuts down, displaying the F75 fault code.

Similarly, sludge and/or air trapped in the system may hamper the proper circulation of hot water, resulting in the F75 fault code when the boiler shuts down.

·        There Are Some More Serious Issues With The Boiler

While mostly the F75 fault code appears due to one of the above-mentioned reasons, sometimes, not so common, it may also happen due to some more serious underlying issues with the boiler, including:

1.       Blockage in pipework.

2.       Internal leaks in the boiler may cause a drop in water pressure.

3.       Problems with the electrical wiring.

4.       Communication errors in PCB (Printed Circuit Board).

Although such problems quite rarely result in F75 code, they can only be detected by a qualified professional boiler engineer. 

How to Clear the Vaillant F75 Fault Code

Here is a step-by-step guide to clear the Vaillant F75 fault code error:

·        Check The System Water Pressure

The normal cold boiler pressure should be somewhere between 1.0 and 1.5 bars. If the pressure is below the normal range, it needs to be topped up. Boiler pressure can be topped up quite easily by homeowners using the filling loop. The filling loop is a braided hose, located under the boiler, with valves on both ends. Pressure can be topped up by opening both the valves and closing them once the desired pressure is achieved. If no other problem exists, it should clear the F75 fault code.

·        Reset The Boiler

Sometimes, this code can be cleared just by resetting the boiler. A reset button is provided with almost all modern boilers. Locate, press, and hold it for 3-5 seconds. The display panels go blank, and soon after that, the boiler restarts. If there is no other underlying issue, the F75 code will be cleared, and the boiler will run normally.

·        Bleed Radiators

In many cases, the F75 error code can be cleared by bleeding the system to remove trapped air. Bleeding can be done with a radiator key. First, bleed the radiators on the ground floor, then those installed upstairs. Once bleeding is successfully completed, the system may require a pressure top-up, which can be performed as explained above.

·        When To Call a Gas Safe Engineer

If none of the above actions work, it is time to call a Gas Safe-registered engineer, as a professional inspection of the pressure sensor and pump may be required.

FAQs

1.     What are the common reasons for the F75 fault?

Basically, it happens when the boiler fails to detect a pressure rise, mostly due to a faulty pressure sensor, a faulty pump, airlocks, or low pressure.

2.     Can I clear the F75 error by pressing the reset button?

Yes, in most cases, pressing the reset button can clear the F75 code if there are no other underlying issues.

3.     Is the F75 fault error dangerous?

Not really; it is a result of an auto-safety step by the boiler to avoid damage. But if the problem persists and is not resolved in a timely manner, it may escalate into a serious issue.

4.     Does low boiler pressure always cause the F75 fault?

In some cases, it might indicate low pressure, but in most cases, it indicates a faulty pressure sensor or pump.

5.     When should I call a professional?

If the F75 fault is not cleared or returns after resetting or topping up, it is advisable to call a Gas Safe-registered engineer to thoroughly check the possible faults in the pump or pressure sensor.

Conclusion

Error or fault codes are displayed on modern boilers to warn homeowners that the boiler is experiencing problems and needs proper attention. In most cases, this also results in shutting down the boiler to protect it from any further damage. Each code refers to a specific issue that may differ across boiler models. The Vaillant boilers sometimes shut down while displaying the F75 fault code.

The F75 fault code typically indicates that the boiler fails to detect a rise in pressure when the pump starts. There may be several reasons for this failure, including low water pressure, a faulty pump, and, more importantly, a faulty pressure sensor. In most cases, this can be cleared by homeowners themselves, but in more serious cases, they may need to call a Gas Safe-registered engineer.