🕑 6 minutes read

What does the Vaillant F75 fault mean?

The Vaillant F75 fault appears when the boiler cannot detect a pressure change after the circulation pump starts. In most cases this points to a faulty pump or a failed water pressure sensor.

Less commonly, a leak or restriction within the heating system may also trigger the fault. The boiler may lock out and stop providing heating or hot water until the problem is repaired.

For a wider overview of common error codes, see our Vaillant boiler fault codes guide.

Vaillant F75 boiler fault complete guide with wall-mounted Vaillant boiler
Get lightning fast quotes. Alternatively, we do offer site surveys where needed.

What causes the Vaillant F75 fault?

Several faults can trigger the F75 error.

Faulty boiler pump

The circulation pump moves hot water around your heating system. If it fails or cannot build enough pressure, the boiler cannot detect the expected pressure increase and displays the F75 code.

Faulty water pressure sensor

The pressure sensor measures changes in system pressure when the pump starts. If it becomes blocked, worn or fails completely, it may incorrectly report no pressure change even when the pump is operating.

Air or debris in the heating system

Sludge, magnetite or trapped air can restrict water flow and affect pressure readings. This can prevent the boiler from operating normally.

Incorrect pump speed

A faulty speed sensor or pump control issue may prevent the pump from running at the correct speed, resulting in an F75 fault.

Pipework leaks

Although less common, leaks within the heating system can reduce pressure and contribute to this fault.


Which Vaillant boilers show the F75 fault?

The F75 fault is commonly seen on several Vaillant models, including:

  • ecoTEC
  • ecoTEC Plus
  • ecoPro

Regardless of the model, the fault means the boiler cannot detect the pressure increase expected when the pump starts.

How to diagnose a Vaillant F75 fault

You can carry out a few basic checks before arranging a repair.

  • Reset the boiler using the reset button.
  • Wait for the boiler to restart.
  • Run a hot tap and listen for the pump — a healthy pump usually produces a low humming sound with slight vibration.
  • If there is no pump operation, the pump may have failed.
  • If the pump runs but the boiler still locks out with F75, the pressure sensor is often the cause.

If your boiler continues to display F75 after resetting, further diagnosis should be carried out by a Gas Safe registered engineer.

How to tell if the pressure sensor has failed

If hot water cuts out while the pump appears to be running normally, the pressure sensor is a likely cause.

Over time, debris and magnetite circulating through the heating system can clog the sensor. Once this happens it cannot accurately detect pressure changes.

Cleaning the sensor is sometimes possible, but replacement is usually the more reliable and cost-effective repair. Homes in hard water areas may also experience limescale build-up that affects sensor performance.

How to fix the Vaillant F75 fault

Start by checking for visible leaks around the boiler and pipework.

You can also try resetting the boiler. If the fault returns, the underlying issue still needs repairing.

Most F75 faults require replacement of either the circulation pump or the pressure sensor. These repairs should only be carried out by a Gas Safe registered engineer. DIY repairs inside the boiler are not recommended.

How to prevent the F75 fault returning

Regular maintenance reduces the chances of recurring faults.

Annual boiler servicing

A yearly service helps identify worn components before they fail.

Check boiler pressure

Keep the system pressure within the manufacturer's recommended range, usually around 1 to 1.5 bar when cold.

Powerflush the heating system

A professional powerflush removes sludge and magnetite that commonly damage pressure sensors and restrict water flow.

Bleed radiators when needed

If you regularly need to bleed radiators, there may be an underlying system issue worth investigating

Need help with a Vaillant F75 fault?

If your boiler continues to display the F75 fault after a reset, it is best to arrange a professional inspection.

Serviceteam's Gas Safe engineers diagnose and repair Vaillant boilers across London. We can identify whether the issue is the pump, pressure sensor or another heating system fault and recommend the most cost-effective repair. If the F75 fault keeps returning after a reset, book our boiler repair service in London for a full diagnosis.

Get lightning fast quotes. Alternatively, we do offer site surveys where needed.