The unit could run perfectly for a day and then shut off.most time it doesn't start in morning after set back thermo turns it on in the morning. The light is blinking 3 times which is pressure switch. I changed draft inducer motot which was defective.sometimes it didn't start because (probably capacitor)vibrated with turning until I started turning it.the new one which I got is a pachard and after a week the plastic cover or fan at rear end of motor fell off.Maybe it is a motor cooler.not sure if it is really important but don't think it is the problem. I tried jumping pressure switch wires but unit wouldn't start. Not sure if contacts on pressure switch are normally closed or open. Forem said cracked heat exchanger but don't want to believe that and sometimed it works fine
Any help appreciated
Thanks
Paul