Well, you stated that the W/H fires up on propane and then slowly dies as if you were running out of propane. You also stated that all of your other appliances work ok. Since the W/H will fire again after sitting for awhile, it still seems like a gas volume/flow issue to me. Either a regulator issue, safety valve issue or perhaps some sort of debris is restricting the flow of gas. I'm assuming you have already checked for spider webs or bugs in the gas orifice. I'm out of ideas. Hopefully someone will jump in with your answer
