Hi, welcome to Just answer
How old is it ?
F4 in Glow worm 30sxi is ignition fault
yes that is what I was writing :)
No problem, I understand....this error is caused when the boiler tries to ignite and fails...the control will then shut the boiler .. you can try to top the pressure up by turning the tap slowly anti clockwise...and when the pressure will reach out around 2 bars then try to close it...this should reset the unit
please let me know how it goes