What temperature does propane stop flowing?

down home wrote:
probably not the case here but another thing to be watched.
Some suppliers not only put propane int their tanks but butane and other heavy and light ends. Works ok in warm weather but you are shortchanged since they don''t have the same energy. When colder the "propane" may not flow too well or at all.
Sometimes it pays to ask and make sure. Others the people filling the tank don't know.

bigger issue is that butane has a much higher boiling point and lower vapor pressure. If you can't get it to boil then no gas.

There is a difference between "propane" and LPG "liquified petroleum gas". propane is propane only. LPG can be either pure propane or a mix of propane, butane etc.