F75 Vaillant Fault Code: Causes and Troubleshooting Guide

The F75 fault code is one of the most common Vaillant boiler problems and relates to pressure issues. The EcoTec Plus and Eco Pro 28 boilers are the most likely to display this fault.

In this guide, we’ll walk you through the causes, solutions, and costs to fix the F75 fault code on a Vaillant boiler. Read on to find out more!

What Is the F75 Vaillant Boiler Fault Code?

The boiler manual lists the following potential causes of the Vaillant F75 fault:

Water pressure sensor and/or pump defective, air in heating installation, too low pressure in boiler; connect external expansion vessel to return.

The boiler itself could be working correctly, but the F75 fault error code may point to 1 of 2 things:

1. The boiler’s pressure sensor.
2. The central heating pump.

The diagnostic process of the F75 fault is not particularly easy, and it’s easy to miss other related faults in boilers. So, if in doubt, you’ll need to contact your boiler care helpline or find a Gas safe engineer.

Faulty Pressure Sensor Causing the Vaillant F75 Error Code

The Vaillant EcoTec range boiler is constantly being developed. Part of the reason for this is that the earlier boiler models had some very poorly made parts. And, one of these previously faulty parts was the pressure sensor inside the boiler.

Since the original EcoTec boiler was launched, there have been 3 major overhauls of the EcoTecs’ pressure sensor. So, luckily, the newer boiler models are much stronger and more durable. If you have an EcoTec that is from 2005-2010, it likely has an older (less reliable) sensor, and there is a good chance it has failed — which is why you’re getting the F75 on your boiler.

But what makes this boiler error develop?

Debris is a major killer of boiler systems. This includes sludge and lime scale.

Prevention methods include installing a scale reducer, magnetic system filter installation and ensuring the system is dosed with inhibitor.

It may be (especially if no fault prevention methods are in place) that the sensor on the boiler has become blocked with debris.

Malfunctioning Boiler Pump Causing the F75 Fault Code

One of the most popular manufacturers of boiler pumps today is Grundfos. They are strong, durable, and reasonably priced for all different types of boilers. Manufacturers such as Vaillant and Glow-Worm use them in their boilers as standard.

Unfortunately, the older Vaillant boilers used an inferior pump. The brand, Wilo, has slowly declined in reputation, as their pumps have become known for failing well before they should. If you have an older Vaillant EcoTec boiler, it might have a Wilo pump installed, and that’s what’s causing the problem, and the F75 on your boiler.

How to Diagnose the F75 Vaillant Fault Code

Start by Checking the Boiler Pump

The easiest way to diagnose the F75 fault code is to start with the pump. If the pump is working correctly, the problem is likely caused by the pressure sensor.

When a boiler fires, a heating pump will kick into action. This will circulate the water around the pipe-work and central heating system.

You’ll recognise the noise as a soft humming noise, and it’s likely you’ll feel the boiler vibrating slightly. If there is no noise or vibration, then the pump is probably not operational, and you’ll need to fit a replacement pump.

Next, Check the Pressure Sensor On Your Boiler

If there’s noise and vibration, the F75 fault most likely concerns the pressure sensor on your boiler. A Gas Safe boiler engineer can fix this by cleaning out the sludge in the boiler. But the time it costs in labour means it makes more sense to replace the whole sensor with a new one.

How Much Does it Cost to Fix the Vaillant F75 Fault Code?

Costs of replacing both the sensor and pump on your boiler will vary. The variation in price will come from:

1. The cost of parts depending on the type of Vaillant boiler you have.
2. Ease of the job. Boiler engineers can access some boilers with less difficulty than others, and this reduces labour time (and cost).

Typically, it costs £240-300 to replace a faulty pump with a top brand like Grundfos. Meanwhile, expect to pay £185-240 for a new pressure sensor. You may find that the cost of replacing your boiler is a wiser investment if the appliance is old, out of warranty, and breaking down often.

Vaillant F75 Error FAQs

Below, we’ll answer some common questions about the F75 fault on Vaillant boilers.

What does F75 on a Vaillant boiler mean?

On Vaillant boilers, the F75 code means that no pressure change is detected when the pump starts working. This could be either because the pump isn’t working properly, or the sensor tasked with monitoring the water pressure is faulty.

How do I fix error code F75 on a Vaillant boiler?

First, you’ll need a Gas Safe boiler engineer to establish which part is causing the error code, as it could either be the pressure sensor or the pump.

Next, the faulty part should either be repaired (if a simple fix is possible) or replaced.

Finally, you can reset the boiler to get it working again.

How do I reset my boiler?

For most boilers, including those manufactured by Vaillant, the reset procedure is rather simple. All you need to do is press the reset button — which is typically located close to the boiler’s display — and hold it for 3-5 seconds. Doing so should clear any error codes on the boiler’s display.

You may have a boiler model that allows a reset to be performed with a knob instead of a button. In this case, you’d have to turn the knob to the “reset” position and hold it there for 3-5 seconds.

Note that simply resetting a boiler will not eliminate the problem that caused it to lock out. Therefore, resets should only be performed after the underlying issue has been fixed.

How do I check the pressure on my Vaillant boiler?

Depending on the boiler model you have, the pressure gauge will either be analogue or digital. If it’s the former, then you’ll have to look where the needle is pointing on the dial, which typically ranges between 0 and 4 bar. If it’s the latter (i.e. a digital gauge), then the pressure reading will show up, in bar, on the display.

Ideally, you’d want your boiler to be operating at around 1-1.5 bar. In most cases, your boiler is leaking water if the pressure drops below 1 bar.

What’s next? Still need help or have questions about your boilers?

Got other Vaillant problems? We’ve covered the F22, F27, F28 and F29 error codes here, and here we’ve got the Vaillant f61 fault code.

Or, if you have fault codes that are not listed, leave a comment and we’ll respond as soon as we can.