My gas furnace ignites for a few seconds then it stop. It does this cycle 4/5 times then locks out. Blower works fine in "on" or "auto". Red light flashes by the ignition module after it locks out. I pulled out the tube at the pressure switch (one tube, two wires model) and the red light turns off. Is this a pressure switch problem?

Clean the flame sensor with some sand paper. Flame sensor located next to or near ignitor.