does anyone know why my pellet stove has just started getting really hot on the top of it and just shuts down it cools off and then it has to be restarted I bought this used and it has been great up until the last couple days it started doing this HELP it only has settings 1,2,3,4 and the fan is on high to keep the house warm it has been about 3 below zero or lower at night any help would be appreciated