F1 is caused by no gas or no detection, also known as lockout. Could be gas filter blockage, flame sense electrode, or pcb.
get the user manual here.:-
http://www.glow-worm.co.uk/manuals/pdf/24ci-18si.pdf
please note , if you are in UK it is illegal to break into any gas connection unless you are qualified to do so.
Pete, February 2007
