I assume this is a permanent pilot, press and hold button and flick striker until it lights, holding button for a further 20 seconds or so? From what you're describing the problem is almost certainly with the thermocouple which establishes when the flame is present then holds the gas valve open. Sometimes the thermocouple fails and needs to be replaced (not too expensive and quite quick), sometimes it's just some corrosion where the connection is made to the gas valve and this can be sorted by disconnecting the couple at the valve and giving the end a light rub with a plastic kitchen scourer. Refit and see if that has cured it. If not get a replacement. I reckon on replacing couples every three to five years.
Andy, December 2005
