I recently had a problem with our Hayward H250IDL2 heater. It showed an "IF" code, which stands for Ignition Failure. I do my own maintenance when I am able to, so I pulled the covers off of the unit and started trouble shooting. I did not manage to resolve the problem, so I called my local pool service company. The tech quickly found the problem: spiders had built their little webs in the small, brass gas nozzles! There are four nozzles, and two of them had webs in them. The tech cleaned these out easily, reinstalled them, and tested the heater. It lit off and ran fine! He told me that, in this part of the country, this is a common problem, and usually occurs as fall approaches and the night time temperatures start to get cooler. Plus, he said the spiders love the smell of natural gas!
I wanted to pass this along, because I had searched for solutions to the "IF" code problem, and never found this mentioned. So...now you all know. It's a quick and easy DIY fix.