You could do worse than contact these people
http://www.espares.co.uk/contact
You may be able to check the gas valve is actually getting an "open" command and eliminate anything upstream. If it is mains powered, a (very) low wattage bulb should be fine - maybe a 240V LED bulb in a holder and a couple of flying leads but BE CAREFUL. If you are not confident you understand what you are doing, find a techie chum
XXX, July 2016