Minimax 400 pilot question

I just bought a home with a pool that hasn't been maintained in years. One of the problems is the heater. I have a general question about a Minimax 400 heater with electronic ignition. I am troubleshooting an issue with the pilot not lighting, and do not see how the unit knows when the pilot is lit. I do not see a thermocouple or any other flame sensing device to let the gas valve know when a pilot is actually lit to allow the main gas valve to open up. I contacted Pentair customer support and he did not know either. He said he would have to ask his heater expert and get back with me. Can anyone tell me how this works?

Long story short, the pilot burner is the flame sensor also. The spark wire also sends another signal and when there is flame present the IID device can sense flame and proceed with the ignition process.

Thanks for the reply. I'm guessing the pilot senses a pressure drop when the pilot is lit. I replaced the pilot burner tip assembly, which included a new ignitor, and the pilot tubing (I broke mine trying to remove it because it was corroded at each end) and it is working now. I'm glad that was all it needed.