you may want to check that the ignitor is free of any debris and maybe lightly sand it with some sand paper and make sure when it arks it looks like a spark plug on your car or lawn mower, and if that is not it, then the gas valve may be bad and not letting any gas come out to ignite the flame when the thermostat calls for heat. Thompson Refrigeration Heating & Cooling if you have more questions. good luck to you.