I have a Pentair Minimax 400 NT heater. It was giving me an E-04. The blower wasn't really moving any air so I replaced it. The heater worked for about 4 minutes and popped the code again.
So I changed the air flow switch. No change. I jumped the air flow switch, after the blower started and voilą, it works. I put a little suction on the hose and again, it works.
Could it be a bad blower motor? Also, when I changed the blower motor there was some heavy caulking around the hood. Could the lack of that caulking be the problem?