You should be able to narrow the problem down to a particular component, but it may be difficult for you to obtain a replacement for the faulty bit, even if it is in effect an electrical rather than gas path issue, because many suppliers insist on selling gas appliance related parts only to licensed personnel. Therefore you may find that you have no option but to get the assistance of a registered technician - engineers deal with the wider infrastructure and are unlikely to be available to do this sort of thing, they do not generally deal with individual appliances or the public for that matter. They are also likely to be even more expensive than technicians.