How to Fix an F75 Vaillant Boiler Pressure Sensor Fault

Last updated on October 6th, 2024

The Vaillant boiler F75 fault code, and all Vaillant boiler fault codes, show on the display when there is a problem and your boiler locks out. Vaillant uses them to show you what might be wrong.

I have been a full-time heating engineer repairing boilers for over a decade and having fault codes on the screen when I arrive is very welcome.

What Does F75 Mean on a Vaillant Boiler?

The F75 fault code (same as Glow-worm F75) most likely means there is a problem with the water pressure sensor.

The pressure sensor measures the pressure of your central heating system. Water pressure sensors can get blocked with dirt and debris from a dirty central heating system. When it is blocked, the pressure gauge will not move when you repressurise your boiler. This will cause your boiler to lock out and show the F75 fault code to prevent damaging the boiler.

How to Fix F75 Fault

To fix the F75 fault, you must replace the water pressure sensor. Sometimes you can remove and clean the old dirty sensor, but most of the time it needs to be replaced.

You should clean the heating system also, as a new water pressure sensor will probably get blocked on a dirty central heating system. Having your system flushed and fitted with a magnetic filter will clean and protect your central heating system for many years to come.

Pressure Sensor Replacement

How to replace the water pressure sensor:

1. Isolate the electric supply to the boiler
2. Isolate the flow and return valves under the boiler and drain the boiler from a drain off on the flow or return. Or, you can drain the central heating system
3. Remove the casing from the boiler and pull down the panel
4. Remove the screw on the black plastic air inlet pipe then pull away the pipe
5. Remove the clip from the pressure sensor and pull the sensor away from the pipe
6. Remove the electrical connection
7. Connect the electrical connector to the new pressure sensor
8. Fit the new sensor and refit the clip
9. Refit the casing on the boiler
10. Close any drain-off valves
11. Open the flow and return valves if they were closed
12. Turn the electric supply back on
13. Check the pressure and repressurise the boiler if the pressure gauge is showing less than 1 bar
14. Turn the heating on to make sure all is good

Pressure Sensor Location

The pressure sensor is located on the main copper heating pipe on the left-hand side of the boiler. You have to remove the boiler casing to access it, and it is quite hard to find and access at first.

How to Clean a Pressure Sensor

To clean a water pressure sensor on a Vaillant boiler, you will need to drain the boiler and remove the sensor as if you were replacing it. Once it is removed, use a tiny screwdriver, or a thin pointed tool, and poke it in the hole in the sensor and scrape it around.

The dirt that accumulates in a water pressure sensor hole, and eventually blocks it, is solid dirt and hard to remove, sometimes impossible. That’s why I don’t recommend cleaning a sensor. You can buy a new one for about £25. The amount of work involved in cleaning it is more than replacing it, and you might not get it to work again.

Vaillant Fault Reset

The first thing I would check on a boiler that is not working, no matter what fault code is showing, is to check the pressure and reset the boiler. Resetting it is the simplest way to get your boiler working again, as it might have just locked out.

To reset a Vaillant boiler, you must find the reset button. This is usually a flame with a line through it. You have to press the button to reset the boiler. Sometimes you have to hold it down for 3 seconds, but on some Vaillant boilers, it just needs to be pressed.

Vaillant Boiler Guides

• Vaillant boiler not firing up
• Vaillant boiler no hot water
• Vaillant boiler leaking
• Vaillant F54 fault
• Vaillant F22 fault
• Vaillant F28 fault
• Vaillant F83 fault
• Vaillant F29 fault

Summary

Replacing a pressure sensor on a Vaillant combi boiler is easy for anyone who has done any kind of boiler repairs before. The F75 error is a good sign that your heating system is dirty and should be cleaned after replacing the sensor.

Feel free to ask any questions in the comments below, and I’ll do my best to help. If you found this post helpful, please consider sharing it.