Flame will come on at first start then will run for a few mins then turn off then ignition will come on but gas will not turn on

Cool you recognize the fact that the igniter is turning on you are obvisouly tech savy so I will dispense with the usual amenities and give you a technicians answere.. igniter gets power and when it reaches max current opens gas valve as time goes on igniter still glows red but doesn,t generate enough current to open gas valve change the igniter first (cheap) if it doesent work check your gas pressure ( need a guy with a special meter) if pressure is too high ( not very common) valve has trouble over comming pressure to open if pressure is ok then time to change out main gas valve Good Luck