Arrived at customer house. Assessed the situation and determined a very dirty filter. I asked the customer when was the last time he changed the filter, he told me never. I explained to him that for this reason the "Open pressure switch" error returned to his furnace. He told me that he understood, I wonder what the solution was, I explained to him about the Media Filter. He told me that he was going to talk to his wife and that he was going to call GGEHS the other week to make an appointment.