I have an intertherm propane furnace, new in 2006 we just turned propane back on for the year, and it won't light. The red light is blinking 2 times & indicates "pressure switch open with inducer on" however I have no idea what that means or how to troubleshoot to fix. It hums like always before it kicks on, but there is no flame. Propane is on, ignition switch is on... any ideas? Please Thank u