My Weber Summit Grill is new. Works fine with new LP tank. When tank is half full grill lights but does not heat very high. Have had this problem with multiple LP tanks.

Sometimes in colder weather, if the tank is less than full the gas can settle. Close the tank valve and unscrew the tank hose connecter. Turn the tank upside down several times and then reconnect and try lighting it up. That is usually fixes it.

IS PROPANE TANK RESIGNED TO BE MOUNTED VERTICAL OR HORIZONTAL? The Outflow tube of the vertically mounted tank runs to within an inch of the bottom of the tank. The horizontally mounted Tank Design has an outflow tube that has a 90 degree bend half way down to 1" of the side of the tank if it mounted in the wrong orientation for it's design, it stops picking up LPG halfway down. When used in it's proper application, the orientation would be correct for gas pickup. A tank designed for horizontal mounting used in a verticle position picks up LPG for half of the tank, then it will light (because of the fumes are flammable) but do not posses the density to heat. (Too much Air) in the mixture fuel to air ratio. We found this out after pulling the shut off valve off of a tank with same problem. It was a horzontal tank used in a verticle positiuon. It worked for half a tank of fuel.