Patio heater won't stay lit

Our patio heater lights and starts heating up, but after 1 -3 minutes it shuts down. The tank is full of propane.
Nexgrill Outdoor Patio Heater Model 920-0010 bought at Costco Talking with Nexgrill tech. dept. as I am writing this.  My problem is similar in that after having the pilot light lit for a minute and then turn the control knob to fire up the burners, the pilot light fades away and then the burners shut off. They suggest it may be the thermocoupling.  The best way, they say, to check to see if it may be defective is to unscrew the thermocoupling from the lower cone cylinder and hold a lighter to the thermocoupler while you turn on the burner (of course you should probably have a lighter for both the burner and the thermocoupler).  The thermocoupler should sense the heat and therefore keep the flow of propane going to the main burner.  If the main burners shut off, most likely the thermocoupler is bad.  I have had great success with Nexgrill's tech. dept.  They are very helpful, keep a good log of your discussions and send out the parts you need, even if you are past the one year warranty period.  I like the Heater but find that any propane device is fraught with issues such as corrosion, leaks, thermocouplers going bad and of course, air not purged from tanks!  Pain in the A----!! Good luck!