Went on a service call today to replace a circuit board that had a bad blower relay in it. Got the new board installed, ran some test runs and furnace was operating normally. When i put the top cabinet cover back on the burners went out and a pressure switch error showed on the diagnostic led. I remove the cover, reset the furnace, and it ran normally again. Until I put the cover back on. I checked the intake pipe for blockage and it was clear. Checked the drain hoses and trap and they were clear also. I don't know how long this has been an issue with the furnace. I ended up leaving one side of the cover a little loose to allow more air intake into the cabinet and it ran normally after that. Is it a bad pressure switch, plugged secondary, or could it be something in the new circuit board? Any suggestions?