Hi, Guy, Sounds like the thermacouple not working, simple test is, can you see that the tip is in the flame, & glowing red before you let the knob out, if it is, & flame go's out instantly, then it's most likely to be 'Kaput' (it's a safety device that shuts of the gas if the flame gets blown out) you can buy a new thermocouple from your locul caraven spares outlet.
mee84, July 2010