Patio heater

There must be a blockage in the hose and regulator or your large tank may be checking and not allowing the unit to stay lit. Remove the large bottle. Let the gas line equalize for about 30 seconds and then reattach the bottle. Very slowly, open the knob on the large tank and I mean very slowly. Did I say open it slowly. The new OPD propane tanks often have a very touchie excess control valve that won't allow enough gas through if opened too rapidly. Now tray and light the heater. If you still experience the same, get a technician involved so they can inspect the gas pressure.