[HayZee518]

that screw is for emptying out the float chamber when you do servicing. my attached drawing will show the insides of the float chamber. there is a black very fine threaded screw in the tang of the float. by adjusting this screw in or out, you are adjusting how high or low the float needs to travel to open or shut the needlevalve.counter clockwise opens the valve - clockwise closes it more. unless you intend to spend some time with the heater don't touch the screw. I found out the hard way.