I bought this propane heater used at a sale a few years ago, and have used it on several jobs. It's a Sure Flame model 1505, 1,500,000 BTU, and puts out some serious heat. It has a two stage operation, seems to work fine on low flame, but on high flame it will burn for 4 or 5 minutes and shut down, as if it is starved for fuel. I have it hooked up to 3- 500gallon propane tanks and all tanks are full. Don't know much about regulators, but the guy from the propane company changed the regulator this morning, didn't help. He says I have 10psi at the tank regulator (it's red) and 1/2psi at the heater regulator(it's gray). It puts out plenty of heat on low flame, and I have used it that way for several winters, but need the extra kick occasionally. Any ideas what I need to check? I'd say this problem is why United Rentals put it in the (as is) equipment sale.