Glow-worm F22 fault

Glow-worm Boiler F22 Fault: Low Pressure

Last updated on June 10th, 2024

The Glow-worm F22 fault code, like the Vaillant boiler F22 fault, indicates low boiler pressure and must be repressurised to fix it.

The first thing you need to do is check the pressure gauge and if it’s low, repressurise it until it’s at 1.5 bar.

I have been repairing boilers for over a decade and this is how to fix an F22 fault.

Glow-worm F22 Fault

It could be other problems causing the F22 low boiler pressure fault code, but a leak is by far the most common reason for your pressure dropping. You must repressurise the boiler to get it working again.

The F22 error should disappear when the boiler is repressurised, and you will hear the pump start to circulate the water in the boiler.

F22 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.

Glow-worm boiler mode button

Knowing how to reset a boiler is the simplest way to get it working again, as it might have just locked out.

To reset a Glow-worm 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 Glow-worm boilers, it just needs to be pressed.

F22 Error Keeps Happening

If you keep having low boiler pressure, showing F22 and going to lockout, then you most likely have a leak on the boiler or central heating system which needs to be fixed.

Or, if you have bled a radiator, then the pressure will drop and the boiler needs to be repressurised.

If the boiler pressure is dropping straight away after repressurising, then you must have a serious leak on the central heating system.

This will need to be found and fixed to get your boiler working again.

Other Causes for an F22 Fault

Other causes for the error code, if it’s not low water pressure, could be:

  • Pressure sensor
  • PCB

How to Repressurise a Glow-worm Boiler

To repressurise a Glow-worm boiler, you must find the filling loop. If it’s a built-in filling loop, it will be under the boiler and probably have a blue knob.

It must be turned anti-clockwise to open and then closed when the pressure reaches 1 to 1.5 bar.

If it’s an external filling loop, it will probably be on two of the pipes under the boiler. It will most likely have two valves with black handles and a flexible hose connecting them.

Filling loop open
Filling loop

You must open both valves to repressurise the boiler, then close them both when it is repressurised.

You should be able to hear the water filling the central heating system when both valves are open, if not, then the filling loop might have problems or the house’s mains water might be turned off.

Boiler Pressure Gauge

The main Glow-worm boiler pressure gauge is a digital pressure gauge on the screen on the front of the boiler. You have to press buttons to find and read it.

Glow-worm boilers have annoying manual pressure gauges which don’t have any numbers on them, so most people don’t know if it’s on the correct pressure.


The F22 Glow-worm fault code is almost certainly caused by low boiler pressure. You must repressurise your boiler to fix the problem and clear the fault code.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


Why does my Glow-worm boiler keep losing pressure?

Your boiler keeps losing pressure because you most likely have a leak on your central heating system, which could be at the boiler.

Another reason your Glow-worm boiler keeps losing pressure could be an expansion vessel problem, or the pressure relief valves might be letting by.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

    View all posts
Share this post

4 thoughts on “Glow-worm Boiler F22 Fault: Low Pressure”

  1. Glow worm betacom 30c
    I’ve got a fault code F22,
    but the pressure gauge is at 1.5. Boiler won’t fire up on heating, but does for hot water.
    I drained system down and refilled it after removing a radiator. I’ve bled the radiators
    Any advice would be great

  2. Hi,
    I have a Glow-worm flexicom HX boiler which is on an open vented system. Each time I have had a power cut when I reset the boiler it tells me There is a F22 fault.
    I have always managed to get it working again by resetting and using different start up methods and then the system work ok till the next time the power goes off. Any ideas what is causing this problem?

    Kind regards


    1. Steven Reid

      Sounds like an external power supply problem, not the boiler.

      1. Thanks for your reply.
        Def. not a power supply problem.
        Boiler tries to fire up a couple of times snd then shuts down and tells me there is low pressure in system,I eventually get it going manually.
        Its been running fine since the power cut
        Bit of a mystery.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top