Hayward 250 BTU Pool Heater Electronic Ignition showing code IF

[ammody]

I am trying to get my heater going for the season, but it stops after few attempts and shows error code IF. I opened up the main gas valve, filter is running and enough water pressure.

The pool was closed last year by professionals. Are there any other things that I need to do in order to make the heater work?

Thanks,
Ashish