All modern grain and pellet appliances have electronic control boards. These control boards are esentially mini computers and subject to damage from power surges and brown outs. The appliance may continue to function, but may not operate at the manufacturers specified protocols. Simptoms can inclue: over or under feeding of fuel, operate at lower or higher exhaust speeds. etc.. Once this damage has occurred there is no way of reversing the damage, you will have to replace the control board. We recommend that a surge protector with a minimum of 1500 joules be installed on every appliance that has an electronic control board.