Greetings and salutations,
After quite a few smokes on my XL, I had the same problem occur this morning that others here, like Petpoor and Barrycuda reported with their smokers. My smoker has been very good about coming up to temp, but this morning, I couldnt get it to go past 200. It was not too cold, 31 degrees and no wind. SO I looked at the flame, and it was pretty low. I played with the valve and it would not adjust the flame uniformly. It would go high and back down to a low setting. I pushed in on the valve while turning it a couple of times and the valve started working correctly with the flame adjusting higher or lower like it normally did.The temp shot up to 250 almost immediately! I backed it back down to the normal position to hold 225 and it has been working fine ever since.
I dont know if this will help others here having low temp problems, but it was something that never happened on mine before, which could possibly explain the reason others here are having temp problems. If this becomes a recurring problem, I hope Masterbuilt will stand behind their product and make a replacement valves or rebuild kits available.
Petpoor and Barrycuda, give this a try. Turn the valve back and forth while pushing in on it. See if that gets the valve working correctly.