It has a standing pilot and it is on, well you know you have gas anyway.

Mine has power coming in and the pressure switch and an external heater temp switch connected to the pool controller. You could try shorting out the wires leading in to the pressure switch just to be sure and make sure you have 120 or maybe 240 feeding the heater itself. They are pretty straight forward. Does it have any indicators on the front? If they are on you should have power. Mine has two small circuit breakers in it on the right side I did trip one once, not sure how, but it was just a push to reset and I was good to go.