I am trying to get an Hayward H400 natural gas pool heater back into operation. So far I have replaced the control and ignitor circuit boards, and it is now showing IO, Ignitor Open error code when I turn it on.
This is what happens:
1. I turn on the heater and bump the thermostat up high enough for it to start heating.
2. The blower starts for about 3-5 seconds
3. The display panel shows "IO" and the blower runs for another 10 or so seconds
4. The blower turns off, the display panel still shows "IO"
5. It cycles back on after some amount of time, sometimes 15 seconds, other times 2+ minutes
This is the manual:
Any advice on troubleshooting? I could replace the ignitor, but I thought that would be an IF Ignitor Failure error. I looked at the wiring and didn't see obvious problems, but I'm not sure how to further inspect it.