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Joe first step would be to verify the thermopile is keeping the milivolt signal on terminals at valve.Since new, it probably is. Next check gas pressure into valve.If it is good and we have the 750 milvolts to valve you have a bad gas valve.
Let me know what you find. Also if you have a manometer, if we are maintaining the 750 millivolts at valve, check inlet and outlet pressure at valve.