Hi There
OK here's what you do.You need to take off cover there's one screw on each side take those out and the front will raise up. Take a can of air and blow everything clean.around the lines back off it, pilot lite where u see dust. Reason i say this because i got the same heater as yours and i clean it every year before winter to make sure i use it. My heater did the same thing and i clean it and it work fine then i done the same thing every year. I don't have the problem no more. Hope this helps you in the right direction. Thank you for writing to fix ya.
Best regards Richard