From rvtravel.com Iwas sent this in my email box today.
RV Daily Tips Issue 469. September 11, 2014 | RV Travel
RV Daily Tips Issue 469:
Here's a nightmare: It's a cold day, your rig is freezing and you're out of LP. So you refill your gas cylinders, hook them back up, and try lighting the furnace — with no success. It's like you never refilled those cursed LP tanks. What's the matter?
Gas valves on LP bottles can stick "shut"
after refilling, even if the valve handle is opened to full. There are a couple of reasons, and usually it's a simple fix.
Here's how to figure out if your tank is acting out of sorts and not passing gas as it should. Assuming that your propane regulator is equipped for two cylinders and automatically switches over to another cylinder when one goes empty, it's easy to tell if your cylinder isn't opening as it should.
Leave the regulator lever pointed to the cylinder
that still has LP in it and connect your "fresh" cylinder up. Now switch the lever over to the filled cylinder but leave the valve closed. The indicator flag on the regulator should show that cylinder as "empty." If it stays flagged as "OK," then light a burner on your stove to draw gas from the cylinders. Now the flag should indicate an "empty" for your recently refilled cylinder.
Slowly open the valve just a tiny bit. Now the indicator flag should show "OK." Proceed to open the cylinder valve completely. If the flag doesn't show "OK" when you gently open the valve, most likely the overfill protection device (OPD) safety valve is stuck closed.
To resolve the stuck valve
, disconnect the cylinder from your regulator and firmly smack the bottom of the cylinder on the ground, jarring it. There's no need to be gentle about it — smack it hard. This will generally loosen the stuck OPD valve. Now repeat the hookup process as outlined above. This time the flag on the regulator should indicate "OK." Open the valve fully, and be sure to switch the regulator lever back to the other cylinder.
Rapidly opening the valve on a fresh cylinder often results in a stuck valve situation and can be prevented by the "slow and gentle" method of cracking the gas valve. If your regulator flag still shows your full cylinder as empty, repeat the "LP Cylinder Smack Down" routine again. If it still fails to respond, you'll need to lug it back to the LP dealer for help.