The spark generator on my two year old Weber Genesis is kaput so I now light the grill with a butane torch. With all the many gas grills I've owned, going back to the early 1970's, I simply turned on the burners and lit them. I never bothered to close the knob on the cylinder between cooks. Now, frequently no gas comes out of the tank. I'm forced to close & disconnect the valve on the propane cylinder, sometimes several times. How it work is a mystery to me. Have they built in some safety feature recently? What is the correct method for lighting this gril? Thanks!