Vaillant F75 Fault Code - Understanding It and Effective Solutions



The Vaillant brand is renowned for its reliability and efficiency. However, like any appliance, Vaillant boilers may encounter occasional issues, and one of the common challenges users face is the F75 fault code. In this blog post, I’ll delve into the details of the Vaillant F75 fault code, exploring its meaning and providing practical steps to troubleshoot and resolve the issue. 

Understanding the Vaillant F75 Fault Code 

The F75 fault code on a Vaillant boiler is indicative of a water pressure sensor problem. This sensor is a crucial component responsible for monitoring the water pressure within the system. When the pressure falls below the recommended levels, the boiler triggers the F75 fault code to alert users to the issue. 

Possible Causes of the F75 Fault Code 

Low Water Pressure: The most common cause of the F75 fault code is low water pressure. This can happen due to a variety of reasons, such as a leak in the system, or flat / faulty expansion vessel. 

Faulty Pressure Sensor: The pressure sensor itself may be defective, causing it to provide inaccurate readings and triggering the F75 code. If the pressure sensor is defective, it is important that your engineer identifies if something has caused the sensor to become defective such as (the most common culprit) sludge in the boiler. As changing the sensor alone and not addressing the sludge issue will only lead to a temporary repair. Cleaning first is essential. 

As the pressure sensor is an inexpensive part, we replace it once every 5 years on our Vaillant Major Service

Faulty Pump: F75 fault can also indicate that the pump has failed.  

Troubleshooting and Solutions

Now, let's explore the steps you can take to troubleshoot and resolve the Vaillant F75 fault code: 

Check the Water Pressure

Ensure that the water pressure gauge on the boiler displays the correct reading. It should typically be between 1 and 1.5 bar. 

If the pressure is too low, check the boiler's manual to learn how to re-pressurise it.  

Inspect for Leaks

Check the entire system for any visible leaks. Leaks can lead to a drop in water pressure, triggering the F75 fault code. 

If you find a leak, it's essential to address it promptly. In some cases, you may need to hire a plumber

Reset the Boiler

Try resetting the boiler to clear the fault code. Refer to the user manual for specific instructions on how to reset your Vaillant boiler model. 

Check the Pressure Sensor

If the issue persists, I advise that you contact a qualified engineer to check the pressure sensor. They can determine if it needs cleaning or replacement. 

Preventive Measures

To minimise the likelihood of encountering the F75 fault code in the future, consider finding a Gas Safe Registered Engineer who will properly service your boiler on an annual basis.  

From My Own Experience 

Most commonly, when I get called to F75 faults, if it’s not low pressure, it’s the pressure sensor that’s failed due to system sludge / magnetite. The pressure sensor can be cleaned, but because it's not an expensive part, I opt to replace it with a new one. 

Again, if the boiler has been contaminated with sludge / debris, it is important that this issue is addressed, as it will only be a matter of time before the boiler breaks down again. 

Sometimes increasing the pressure beyond its normal standing pressure will trigger the sensor and the boiler will come back on. I don’t recommend doing this but if you’re waiting on an engineer and desperate for hot water and you can give it a try. Be careful not to overdo it, don’t go above 2.5 bar, and don’t use the central heating as this may lead to the boiler exceeding 3 bars of pressure, which will result in further problems.  

Written by : Paul Tozer

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