[bobbecky]

Actually, OPD means Overfill Protection Device, not overflow. Propane tanks can not safely be filled completely, they must have an expansion space. The overflow feature is built into the propane hose pigtails that connect to the tank. There is a spring loaded valve that stays open during normal gas flow, but if a line gets cut, or when opening the tank valve too fast, the valve will close, and there will be gas flow, but not enough to make your heater work. To fix this, you turn off your tank valve, remove the hose from the tank, which allows the spring loaded valve to return to normal, then reconnect to the tank and slowly open the valve.