Since its brand new my guess you have some blockage between the gas flow and the igniter. I had a similar issue where the unit was shipped with an extra little mounting bracket loose in chamber. That little bracket lodged between the gas feed and the spark igniter. When enough gas build up and hit the igniter and the mini explosion occurred. My POS dealer never found it. I decided to take it apart and it was right there plain as day.
Could be nests or something else but that's where I would start. If there is no blockage it's a fault valve or regulator.