Have a Hayward heater and decided to use the spa last week. The heater fan would start and you could hear the ignitor working but it would not start up. gas line outside the heater was open..... I was hoping it wouldn't be one of the boards and got a I F indication on the readout.... I called a gas guy that I used a couple of years ago and he said it could be spider webs and did I smell gas. I replied no and he said that I should open the control module and where the gas comes into the heater there is a knob. I opened it and could hardly see much but felt around and indeed there was something you could turn and sure enough after turning it counter clock wise, I got the heater working. What I find disturbing about this is that I have had the pool for 6 years and never even knew this turn off knob was even there. I also can't believe the pool guys when opening or closing have actually ever shut this down until now..... just odd to me....