If it lights on gas bu t goes out when you release the gas valve(knob)then it will be the thermo couple (about £20)or worst case is the control valve itself(i doubt it though)or try this,take the plastic knob of and press the metal part in and light the gas as normal,hold for 10seconds and release does this work?lif it does put a small amount of paper into the plastic knob where it fits onto the metal part of the valve.(the plastic knob is worn and not pressing the valve home)if this works let me know and i will help with the electrics
mikec
August 2010