Unable to diagnose cause of error. System will intermittently show pressure switch codes with occasional flame loss. Main issue noticed is that thr inducer motor after fireoff will slow down to a point where the pressure switch opens and system will shut off. While inducer motor is at a higher speed during and just after fireoff, pressure switch is satisfied. Attempted to run with burner box door off, attempted to run with the exhaust pulled off. Nothing tested would change to operation of the furnace. System would run for 1-2 minutes before the inducer motor slowed down so much the pressure switch would open. Furnace would only intermittently show codes and control system on furnace would not allow me to lock it into high fire. Due to erattic behavior, suspect it may be the control board, but cannot be certain. We will need to send someone else out to inspect.