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How To Fix Vaillant Fault Code F75?


The F75 Fault Code is well-known to the older generation boiler owners. Specifically, we are referring to the EcoTEC line.

As you might be aware, Vaillant boilers are German work-of-arts. However, it wasn’t always the case. Before 2005, Vaillant almost fell because of their faulty and low-quality boilers. The EcoTEC line almost killed the industry giants. Homeowners all over the world were constantly complaining and writing refund letters.

In their defence, the owners forwarded the blame to their third-party component supplies. A few years later, they recovered and went back to producing high-quality boilers. However, there are forever dark shadows in the marketplace.

The old-model faulty boilers are still well and alive in stores all over the world. If your boiler frequently displays the F75 Faulty Code, chances are, you are a victim.

What is the F75 Vaillant Fault Code?

We thought it would be a good idea if we referred to the official Vaillant boiler user manual. It offers detailed information on the F75 Vaillant Fault Code.

According to the manual, the fault message informs the owner that it can’t detect any pressure. Therefore, it can’t circulate hot water around the pipes and heating system.

From the above statement, we can tell that the pressure sensor has something to do with this. On the same note, we can also suspect something is wrong with the boiler pump.

In conclusion, as the name suggests, the fault code is most popular with faulty Vaillant boilers. It has many possible causes. However, there are two main ones:

  • A faulty pump or
  • A clogged pressure sensor.

Unfortunately, there isn’t much you can do to solve these problems alone. We advise you to call your most trusted Gas Safe registered engineers and have them diagnose your unit.

Causes of the Vaillant F75 Fault Code

We’ll start with the main and most popular causes down to the rarest.

A faulty pump

The pump comes before the pressure sensor.

Not long ago, a boiler-related company known as Wilo was responsible for manufacturing boiler pumps. In part, they are to blame for the low-quality Vaillant boilers produced pre-2005. Thousands of customers lamented on how the pumps were prone to leaking and splitting.

Fortunately, you don’t have to replace the entire pump. It’s a matter of identifying when your boiler was manufactured.

If your boiler has a manufacture date older than 2005, then you’ll have to replace the pump head and entire hydro-block section.

If the manufacture date is much resent, then you’ll only have to replace the pump head.

An easier way to tell them apart is to look at your pump’s data plate. If its background is white, you’ll have to replace the pump head plus the entire hydro-block section. If it’s black, you’ll only have to replace the pump head.

A faulty pressure sensor

Despite the fault code, your boiler might appear to be alright. Most of the time, the pump will be working as usual. However, there is one big problem, you’re no longer receiving hot water, and the radiators aren’t heating up as they’re supposed to.

Boilers are among the most hardworking appliances in most households. Like many other mechanical systems, boilers are prone to dirt and debris buildup. Unfortunately, dirt has a habit of accumulating on and around pressure sensors. The dirt layer is usually so thick that the sensor can no longer do its job.

When the sensor is blocked, it can no longer take pressure readings. If the boiler pressure were to drop, the gauge would not reflect. It will simply stick at a certain point.

The easiest way to test for a faulty pressure sensor is to shut down the boiler. After a few minutes, have someone start the boiler as you pay attention to the pressure gauge. As the pump starts, it should record an increase of at least 0.2 bar. If it doesn’t, then something is wrong with the sensor.

The engineer can fix the problem by cleaning or replacing the pressure sensor (If it’s faulty).

Poor boiler servicing and maintenance

Take it from us, lack of servicing is the “mother problem” for most boiler faults.  Issues that snowball into catastrophic faults would have been identified if the owners were keen and strict about boiler maintenance.

For example, you’ll never have to deal with a dirty and non-responsive pressure sensor. The engineer would have cleaned it before its fault. The same goes for pumps.


Leaks are notorious troublemakers for boilers. They contribute to many boiler fault codes, including the F75.

Most people assume that leaks only happen in pipes. That’s not the case. Leaks can happen on any component with a joint or some space that can allow water to flow.

Once your boiler leaks, its water pressure will drop. Once the pressure drops too low, the boiler will no longer supply and circulate water throughout the system.

Expansion vessel depletion

We know you’ve probably never heard of the Expansion Vessel. It’s an important boiler component that affects boiler pressure. It must fit the unit perfectly. Besides correct sizing, it should also be sufficiently charged.

Professional and experienced heating engineers are aware of this sneaky component. If the charge is too low or very high, it will negatively affect the quantity of positive pressure put on the pressure sensor. When this happens, it triggers the F75 Fault Code.

Clogged pipework

Pipework issues are rare. Nonetheless, if they do happen, they are most likely to be misdiagnosed. For the client, a misdiagnosis might mean spending a lot of money on unnecessary repairs.

Clogged pipework is famous in the older generation Vaillant EcoTECH boilers. This is because they have rubber hose sections on the Flow and Return pipes. Unfortunately, rubber isn’t the best option. Unlike the modern copper pipework, rubber attracts magnetite residue that blocks the system and restricts water flow.

Magnetite residue buildup is the main reason we always recommend magnetic filter installation. It will trap most of the debris before it has a chance of accumulating in your boiler.

Clogged heat exchanger

Although it rarely happens, if you’re facing the F75 Fault Code, you should consider the possibility of having a clogged heat exchanger in your hands. You should consider it more if you find yourself frequently replacing your pressure sensors.

“Power-flushing” is the most effective way of fixing a clogged heat exchanger. It involves forcing a chemically-infused liquid through your central heating system. The liquid will then wash and remove most of the dirt buildup that might be accumulating in your boiler.

A faulty PCB

The boiler PCB does lots of things that we can’t afford to explain in this article. Nonetheless, it’s responsible for supplying the pump with power. For a boiler pump to function well, it needs at least 230 volts. Any amount less than that and the pump will not start.

We’ve seen it happen. Many engineers are quick to write off a pump simply because it won’t start. Unlike them, we’ll try our best not to burden you with unnecessary costs. We’ll only advise for replacements after several intensive tests.


Most of the time, the Vaillant F75 Fault Code tells you something is wrong with your boiler’s pressure. The pump and pressure sensors are the most notorious culprits. Have then checked.

Unfortunately, there’s no way you can fix this problem alone. Leave the sacred work to Gas Safe registered heating engineers.

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