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The first thing I would check is the LP pressure. That is controlled by the regulator at the tank. If the pressure is too low it will have a hard time operating correctly on LP mode. It can also be some debris in the burner area.........either ON the burner or in air intake system for the burner. It might be the working voltage is too low. This is more often when you are dry camping. Please get back to me and explain the "fiddling" part and what you actually did here and I can offer more. Do you have the Owner's Manual for this? That would be helpful here as well. And you said "when I first put it in" so I am understanding it wasn't an OEM installation. Please include what this is in so I know what else you may be dealing with here. All follow ups are included in our fee and fully expected. It can take some "back and forth" to sort this out. Thanks for coming to us here at Just Answer with your question.
Just checking back in, Ian, to see if you were able to get this resolved or do you need additional input from me here?