I have a Amana furnace that quit working and I get three flashing lights that tells me that the pressure switch is stuck open. So when we hold the kill switch in and blow into the tub from the motor end and continue to blow in and out the furnace starts up and we get flame. But when we put everything back together it won't start up again. Is there any way to fix this without a tech. I am thinking could the pressure switch need to be replaced?