Glow-worm F75 Fault Code Repair: Pressure Sensor Problem

Last updated on January 1st, 2025

An F75 Glow-worm fault code shows on the boiler display when there is a problem and your boiler locks out meaning you’ll have no heating or hot water. Glow-worm uses them to show you what might be wrong with the boiler when it’s not working.

I have been carrying out boiler repairs for over a decade and having fault codes on the screen when I arrive is a great help.

What Does an F75 error Mean?

The Glow-worm boiler F75 fault code (like the Vaillant F75) usually means you have a blocked or faulty 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. A blocked pressure sensor means the pressure gauge will not move when repressurising your Glow-worm boiler. This will cause your boiler to lock out and show the F75 fault to prevent damaging the boiler.

How to fix an F75 fault

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

Make sure it’s clean

You should clean the full system when replacing the sensor as a new water pressure sensor will probably get blocked again 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. This will prevent sludge problems like a blocked 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 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

Location

The Glow-worm 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.

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 is the simplest way to get your boiler working again as it might have just locked out. To reset a Glow-worm boiler, you must find the reset button.

Glow-worm boiler guides

• Glow-worm boiler no hot water
• Glow-worm boiler not firing up
• Glow-worm boiler pressure
• Glow-worm F83 fault
• Glow-worm F22 fault
• Glow-worm F28 fault
• Glow-worm F29 fault

Summary

Replacing a pressure sensor on a Glow-worm combi boiler is easy for anyone who has done any kind of boiler repairs before. The Glow-worm 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 any questions in the comments below, and I’ll do my best to help. If you found this post helpful, please consider sharing it.