My sunflower does it too. It's the overflow protection valve. When you crack the valve you must crack it slooooowly. The line has lost pressure since the last time you used it. So if you crack it fast the propane in the tank rushes out to fill the void (no back pressure). The OPV is designed to prevent explosions (opening bottle valve in a building with nothing attached for example). So the valve puts a halt to "no backpressure fast flow"... as it's designed to do. If you listen carefully you can hear the safety valve go "click" as it is forced up by fast flow into the seat where it then halts 95% of flow or some such.
If you then close off any heater flow and the bottle valve and wait you will eventually hear another "click" as the OPV needle thingy drops back down out of the seat because equilibrium has been established (same pressure now exists between the hand valve and your bottle's interior - with the OPV sitting in between the two). Now that there's backpressure you can open up bottle valve slowly letting the tubing also get up to pressure and only then turn on your heater flow. It won't trouble you again until you have low pressure in the hose and are too quick to open the bottle.
the regulator in your heater becomes the new high-to-low pressure regime - pressure equilibrium remains between your bottle and the hose - so even if heater is allowing lots of flow your OPV won't kick in.
hope that makes sense
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Safety Valve , Next time close the valve on the tank and open it again slow.
Ha ha - faster and more succinct than guywhoblabsaboutpressuresflowsandsuchtoomuch
