We have a Raypak RP2100 natural gas heater for our in ground pool/spa combo. When we moved into the house a couple months ago I couldn't get the pilot fired so we called up the home warranty place (included when we bought the place) and they sent someone out for a quick $60 deductible and it ended up being some carbon buildup in the pilot assembly. They purged the line, cleaned the holes, and got it lit within a few minutes. The pilot has stayed lit and we've used it 5 or 6 times since. Fire it up via the switch and crank the thermostat to hi and it works great.
About 2 weeks ago the burner failed to light when I turned on the switch, regardless of the thermostat position. The pilot is still lit but I don't hear any difference in the gas flow when turning on the switch so I'm assuming one of the safety circuits on the regulator is preventing it from opening up fully to supply the larger volume of gas for the burner to fire.
I'm pretty handy once I'm familiar with something but being that this is our first pool as well as our first gas appliance (ever) I'm a little unsure of how to properly troubleshoot the issue. I have no problem calling the home warranty co to come back out and look at it, but I'd rather figure out how to properly troubleshoot and resolve it myself if at all possible.