The gas clicks out on in my Ideal Mexico Super RS 65. What to do?

We have a Gas water heater, an Ideal Mexico Super RS 65. It clicks off a very short time after being ignitied. All the flames go out, inc the pilot. Can get luke warm water after constantly igniting. Have checked the pump, that is, unscrewed the big screw and clear water dripped out. Screwed the small screw inside about 20 times clockwise, turned power on and by torchlight, can see that the inside is whizzing around. Am guessing that the pump is working! The gas is still clicking off after a few seconds. PLEASE advise. Any suggestions, please. Thank you in anticipation.