Last updated on October 28th, 2023
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 with the boiler not firing up.
I have been a full-time boiler repairer for over a decade and having fault codes on the screen when I arrive is very welcome.
In this post, I’ll go through how to fix your F75 fault.
What Does F75 Mean on a Vaillant Boiler?
The Vaillant boiler 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 Vaillant boiler.
This will cause your Vaillant boiler to lock out and show the F75 fault code to prevent damaging the boiler.
How to Fix F75 Fault on a Vaillant Boiler
To fix the F75 fault on a Vaillant boiler, 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 system filter will clean and protect your central heating system for many years to come.
Vaillant F75 Pressure Sensor Replacement
How to replace the water pressure sensor on a Vaillant boiler F75 fault:
- Isolate the electric supply to the boiler
- 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
- Remove the casing from the boiler and pull down the panel
- Remove the screw on the black plastic air inlet pipe then pull away the pipe
- Remove the clip from the pressure sensor and pull the sensor away from the pipe
- Remove the electrical connection
- Connect the electrical connector to the new pressure sensor
- Fit the new sensor and refit the clip
- Refit the casing on the boiler
- Close any drain-off valves
- Open the flow and return valves if they were closed
- Turn the electric supply back on
- Check the pressure and repressurise the boiler if the pressure gauge is showing less than 1 bar
- Turn the heating on to make sure all is good
Vaillant Water Pressure Sensor Location
The Vaillant water 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.
F75 Vaillant Fault Reset
The first thing I would check on a Vaillant boiler that is not working, no matter what fault code is showing, is to check the pressure and reset the boiler.
Knowing how to reset a Vaillant boiler 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 boiler pressure
- Vaillant F54 fault
- Vaillant F22 fault
- Vaillant F28 fault
- Vaillant F83 fault
- Vaillant F29 fault
Replacing a pressure sensor on a Vaillant combi boiler is easy for anyone who has done any kind of boiler repairs before.
The Vaillant F75 error code is a good sign that your heating system is dirty and should be cleaned after replacing the pressure sensor.
Feel free to ask me any questions in the comment section below and I’ll try my best to help.
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How do you clean a water pressure sensor?
To clean a water pressure sensor on a Vaillant boiler, you will need to drain the boiler and remove the pressure sensor as if you were replacing it.
Once it is removed, you should use a tiny screwdriver or a thin, pointed tool. The dirt that accumulates in a water pressure sensor hole, and eventually blocks it, is solid dirt and hard (sometimes impossible) to remove.
That’s why I don’t recommend cleaning a water pressure 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 actually get it to work again.
It’s a bit of a gamble putting everything back together for it not to work and having to replace it anyway.
Where is the pressure sensor on a Vaillant boiler?
The pressure sensor on a Vaillant boiler is on the main copper heating pipe on the left-hand side of the boiler. You have to remove the boiler casing to access it.
How does a water pressure sensor work?
A water pressure sensor on a boiler works by measuring the force on a diaphragm which will switch the boiler off when the pressure is too low or there’s another problem.