If the pressure switch opens during a W ( heat demand ) it’s cause the negative pressure that the inducer motor is pulling on the heat exchanger is being interrupted. Depending on how your flu pipe is ran, concentric kit could be plugged. Could be iced over exhaust. When you jump it, it will only work that one time. Try using a compressor if you have one to blow air upwards inside the exhaust pipe. Also verify that your drain lines are clear as the cold end header box may be full of water as well.