Every summer I have trouble getting my pool heater going. It is a gas heater for my inground pool.

The pilot light is lit, but it won't turn on. I got it to come on once, but never again. It is very sensitive to pressure, dirty filter, ect. So, I have backwashed, and cleaned all the skimmers and pump strainer pump.

Any ideas of what else I can trouble shoot before having someone come out and look at it..?