Propane grill leaking from valve stem
I'm no expert on flammables, but I've grilled a ton in my day on various equipment, and feel I've learned a couple things that may help here.  However, your mileage may vary, and take this all with a grain of salt.

Is this a known problem?

Depends on what this is.  I agree with your read that this likely isn't your equipment, and is likely something on the tank.  If so, it is not known to me, but I have a different approach on tanks than you.  More below.

Should the store I bought it from agree to just replace my tank for free?

Yes, I think they should do so happily; it leaks gas after all.  If they don't, you should insist (say something about how you were hoping to grill some steaks, not start a house fire).  

Is there some reason this might actually be a problem with my equipment?

The only thing I could fathom is if your equipment had some significant downstream pressure, but even if it did, I believe that would cause propane to flow more slowly to your burners, not leak out the back of the tank valve.

Is this a pressure release value?

This doesn't sound like a pressure release valve issue to me.  If it were, the valve would open when the pressure increased inside the tank (usually a function of tank temperature increase), completely unrelated to when you opened the tank valve.

So then what is it?

If I had to guess, I'd say that the bleed screw is not tightened down well.  This screw is opened when they fill the tank (allowing the air to escape while LPG is pumped into the tank).  When they are done filling the tank, the bleed screw should be tightened, and perhaps that wasn't done when these tanks were filled.  With the tank valve closed, check the bleed valve on the back of the tank valve to ensure it is closed.

So what should I do?

For what it is worth, I've never been a fan of those tank exchanges for a handful of reasons:


Partial Fills. Most all of the tank exchanges only put in about 15# (~3.6 gallons) of propane.  Even in warm weather climates you should be able to get 20# (4.7 gallons) of propane into a 20# tank.
Beat-up Tanks. The tanks I see at the exchanges are usually pretty beat-up.  This could be part of what you are seeing, tanks with faulty valves (however, I have to believe they do some level of checking before they ship full tanks back to the retail stores, right?).
Ugly Tanks.  I hate seeing the tank exchange company's brand plastered all over the side of the tank.


I have had excellent luck in buying several new, empty tanks (from Home Depot or the like) and having them filled myself (usually at either a U-Haul, AirGas, or gas station).  It's slightly less convenient, but I get a longer effective tank life (usually 33% more gas in my fill vs. exchanged tanks), better value (the gas is cheaper!), and my tanks don't look nor operate poorly.