Ian just read the problem your having with your boiler and the fault is quite cheap and easy to rectify.
The two pipes you refer to are going to the air pressure switch which is a round unit with wires to it, these often fail as the diapham in them become week or get jambed thus not kicking the gas value open. Taken the air pressure switch out and replace then boiler will work. hope this helps, any more problems then feel free to contact me on brad@hotmail.com
Bradley
August 2006