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Last updated: 22nd February, 2024


Vaillant Error Code F75

Vaillant Error Code F75

Key takeaways

  • The Vaillant F75 error code signifies one of three potential boiler issues - faulty pressure sensor, faulty pump or a heating system leak.
  • It's best to allow a Gas Safe registered engineer to confirm the fault and carry out repairs.
  • Modern boilers are more efficient and robust compared to older models.

One of the most common and frustrating error codes your Vaillant boiler can present to you, the F75 warning represents a potentially serious fault concerning your boiler's function and subsequently its ability to heat your home.

Here at iHeat we’re boiler experts and in this blog we’re going to be taking a look at the F75 Vaillant boiler error code, specifically its meaning, the causes behind this and how to remedy the problem.

What Is An Error Code?

A boiler error code does exactly what it says on the tin, presents the owner of a boiler with an alphanumeric three digit fault detection message (e.g. F75) upon the system detecting something such as an integrated component not functioning as it should. 

Where Are Error Codes Displayed?

An error code can be found on a boiler's display screen which is usually at the centre or near the bottom of the boiler unit, on some models the screen is covered by a folding down plastic panel.

The code being displayed can be identified and further explained in the appliances user manual or on some manufacturer’s app.

Vaillant F75

We are aware of the desire to rectify a heating issue ASAP, especially if the fault has caused the boiler to ‘lockout’ (shutdown to prevent further fault).

The option of simply restarting your boiler may often solve the issue being brought to your attention by an error code… temporarily.

It can prove wise to first fully investigate and understand the cause of the error code, this is the most efficient way of ensuring the issue can be fully remedied, making it less likely to occur down the line.


The Vaillant F75 can be put down to a pressure issue, resulting in the boiler being ‘locked out’.

Manufacturers Vaillant explain the issue to be  - ‘no sudden change in pressure was detected on turning on the pump’.

The two main causes for a pressure issue and F75 error code are:

Faulty Pressure Sensor

The water pressure sensor within a boiler can become blocked over time with a variety of contaminants including debris, dirt and limescale.

This can cause the sensor to perform sub-optimally in terms of reading and reacting to pressure changes.

If the boiler's pump sounded and felt as it normally would when operational, but there was a lack of hot water in the presence of an F75 error code, the fault is more than likely pressure sensor related.

Faulty Pump

Some earlier Vaillant models were claimed to be fitted with poor quality heating pumps, prone to splitting and leaks, two common causes of an insufficient amount of water getting into and out of the boiler, leading to the presence of a F75 error code.

You can confirm the pump is the area of concern if the boiler is switched on, but you can't feel or hear any operational noise.

Heating System Leak

If the pipework has a leak, it will prevent a sufficient amount of water from reaching the boiler, and no pressure will be detected by its sensor.

This problem is the least common of the three discussed, and to confirm its occurrence you must be fully certain the boiler's pump and pressure sensor are both adequately operational.

Fixing The F75 Error Code

For this particular Vaillant error code, it would be unwise to attempt a DIY fix; any of the three potential causes of the F75 would be considered serious and an attempt at an unqualified or inexperienced repair may lead to further function degradation or potential safety issues.

It’s prudent to have an expert, Gas Safe registered engineer to assess the fault and rectify accordingly.

Gas Safe Registered Engineer

This is a fully trained and qualified gas engineer who is legally licensed under the published Gas Safety (Installation and Use) Regulations 1998 (GSIUR).

The Gas Safe Register is the appointed representative of the safety regulatory group- Health and Safety Executive. 

All registered gas safe engineers should carry and be able to present official accreditation and have a verified and unique ID number. 

All of our iHeat engineers are registered Gas Safe!


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 F75 on a Vaillant boiler?

To fix the F75 error on a Vaillant boiler, you need to address the water pressure sensor or the pump's functionality. First, check the system's water pressure and repressurize if it's too low. If the issue persists, inspect and clean or replace the water pressure sensor and ensure the pump is operating correctly. If you're not confident in performing these tasks, it's best to seek assistance from a professional technician.

How do I fix low pressure on my Vaillant boiler?

Fixing low pressure in your Vaillant boiler typically involves repressurizing the system. Locate the filling loop beneath your boiler and slowly open the valves to allow water into the system. Watch the pressure gauge, and once it reaches around 1.5 bar, close the valves. This should resolve low-pressure issues; however, if the pressure drops again, you might have a leak in the system that needs professional attention.

What is the F74 fault on a Vaillant boiler?

The F74 fault code on a Vaillant boiler indicates a specific issue related to the water pressure sensor not detecting any changes in pressure, which could be due to a sensor fault or a problem within the water circuit, such as a blockage or leak. This fault requires diagnostic checks by a qualified technician to identify and rectify the underlying cause.

What is the glow worm on a boiler F75?

The term "glow worm" in the context of a boiler F75 error seems to be a misunderstanding. The F75 error code is specifically associated with Vaillant boilers and pertains to a water pressure sensor or pump issue. If you're encountering an F75 error on a Glow-worm boiler, it's advisable to consult the boiler's manual or contact a professional, as the error codes and their meanings can vary between manufacturers.

What does F75 mean on a Valiant boiler?

The F75 error code on a Vaillant boiler indicates a failure in detecting a pressure increase when the pump is running. This problem is often related to the water pressure sensor or the pump itself. Resolving this error involves checking the system's pressure, inspecting the sensor and pump for faults, and ensuring they are functioning correctly to maintain proper pressure within the boiler.

How do I lower the water pressure on my Glow-worm boiler?

To lower the water pressure in your Glow-worm boiler, first ensure your system is not actively heating and locate the pressure relief valve. Carefully open the valve to release small amounts of water, monitoring the pressure gauge until it returns to the recommended level, typically between 1 and 1.5 bar. If you're unsure or unable to safely adjust the pressure, it's wise to contact a professional.

What to do if Vaillant boiler pressure is too high?

If the pressure in your Vaillant boiler is too high, locate the pressure relief valve and carefully release water to bring the pressure down to the recommended level of around 1.5 bar. High pressure over time can cause damage to your boiler and heating system. If you frequently encounter high pressure or if adjusting the pressure does not resolve the issue, seek professional advice to diagnose and fix any underlying problems.

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.