The Vaillant boiler F75 fault code, and all Vaillant boiler fault codes, show on the screen on the front of the boiler when there is a problem and your boiler locks out.
Vaillant uses them to show you what might be wrong with the boiler. Having fault codes on the screen is a great way to help diagnose your boiler problems.
I have been carrying out boiler repairs for over 10 years and having fault codes on the screen when I arrive is very welcome. Not all boilers use fault codes, so having them is a huge bonus.
What Does F75 Mean on a Vaillant Boiler?
Vaillant boiler F75 fault code means there is a problem with the water pressure sensor. The pressure sensor tells you what the pressure of your central heating system is.
Vaillant F75 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 probably clean the central heating system also, as fitting a new water pressure sensor on a dirty central heating system, will most likely block the new pressure sensor again.
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
To replace the pressure sensor that causes the Vaillant F75 fault code, you must –
- Isolate 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 clip from the pressure sensor and pull the sensor away from the pipe.
- Remove 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.
How to Reset a Vaillant Boiler
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 F75 Fault Code FAQs (Frequently Asked Questions)
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 very solid dirt and hard to remove.
That’s why I don’t recommend cleaning a water pressure sensor, as you buy a new one for £20 or so.
The amount of work involved in cleaning it is more than replacing it, and you might not actually get it to work again, so it’s a bit of a gamble putting everything back together for it not to work and have to replace it anyway.