F75 Vaillant fault – How to fix

The F75 Vaillant fault boiler often indicates a problem with the pressure detection system. The boiler has a pressure sensor that should detect an increase in pressure when the pump starts working. If it fails to detect this increase, the F75 error code will be displayed. There are multiple possible reasons for this issue, and it is likely that you will need the help of a heating engineer to fix it. However, we will explain the cause of the problem and provide repair suggestions that you, as a homeowner, can attempt.

Here’s a list of what could be causing the problem.  

• Faulty pressure sensor – not detecting the increase in pressure.
• Faulty pump not spinning correctly 
• Low water pressure 
• Deflated expansion vessel. 

Firstly as a homeowner you can check the pressure and try resetting the boiler.

Check Water Pressure:

• Locate the pressure gauge on your boiler. It is usually on the front and may have a green and red section. Or it may be indicated on the digital display.
• Check if the needle is within the recommended range, which is typically between 1 and 1.5 bar. If it’s below this range
• Add pressure to the boiler. 

Reset the Boiler

• This is a round or oblong button on the face of the boiler. It will have a flame with a cross through it. Press for 5-10 seconds until the display resets. This may get your boiler working again on a temporary basis. 

If the previous attempts to fix the issue have been unsuccessful, it is probable that either the pump or pressure sensor needs to be replaced. It might also be advisable to have the boiler serviced simultaneously. The engineer should also examine the expansion vessel and add more air if necessary. The pressure sensor is typically priced at £30-£40, making it one of the least expensive components of the boiler. In general, we recommend starting with the pressure sensor due to its low cost, unless it is evident that the pump is not functioning or displaying signs of malfunction. A new pump typically costs £190-£250, with additional charges for labor.

Remember to follow the specific instructions provided in your boiler’s manual, as different Vaillant models may have slight variations in their procedures. If you’re unsure or uncomfortable performing these steps, it’s best to consult a professional to avoid causing further issues or voiding your boiler’s warranty.