I posted a reply on another thread and did not get any response, so I am starting a new thread. I think I read all threads on this topic as I thought I had a similar problem. I get the three blinking lights after the furnace works for a few hours every day and I need to manually reset the furnace. I replaced my pressure switch and I still have the problem. If I shut the furnace off and turn it on, the furnace will light. If I squeeze the tube to the switch and release, it will light. If I take the tube off at the switch and put it back on, it will light. If I take it off and even just hold it close enough to get some vacuum to the switch it will close and light. The furnace is very new and there is no sign of any dirt or moisture anywhere. I replaced the switch because it seemed to me that perhaps it was sticking and needed to be opened and then closed again in order for the contact to be made. Replacing the switch proves it is not the switch. There is plenty of vacuum to close the switch, so it is nothing between the switch and the inducer. What else could it be?