I have had a Pit Boss Grills 77550 5.5 Pellet Smoker for years and never any issues. I recently got two more of them and both are having the same problem. If I set them to 200, 300, 350 or most temperatures they regulate themselves. If I set them to the 400 degree temp they just keep adding pellets non stop until the temp gets so high they shut off like a power loss. ( I assume the control board overheats at this point). Any idea why this is happening? The same smoker I have had for years does just fine at any setting.