How do I get my propane to go through to the furnace?

I almost ran out of propane today and then had propane added to the tank. Now the furnace igniter will light up but then it will make a switching sound and then go off. Also the hot water heater runs on propane and I cannot get the pilot light on it to relight. I think somehow there may be air in the propane line or somehow the fuel is not getting to the furnace and hotwater heater? Any suggestions?? Thank you