Check the Hose
Before purchasing a new switch or determining that your switch is broken, make sure the hose attached to the switch is not clogged. To check this, remove the hose from the switch and blow through it then reconnect the hose to the gray-side port.
Flashing Draft Fan Setting - This indicates that the stove is in normal operation and that the vacuum sensor detects a loss of pressure either because the door is open or because there is a negative pressure in the room with respect to the exhaust. If the problem is not remedied and the unit is still in start-up mode you get a ERR-3. If this problem happens during run mode, you will get an ERR-2.