I have a Hayward H250FDN heater. It will start and heat the water but then shuts down after 60 seconds and displays the AO code. According to the manual this indicates a bad blower vacuum switch. I've checked everything suggested in the manual... the blower, vacuum switch, tubing between the blower and vacuum switch and all associated wiring. All appears to be working like it should. The only thing left would be the ICB. Before I spend $200 on a new one I thought maybe someone on this site may have an idea on something else I could check? Thanks in advance for any help.