Having a problem with a small NG 75000 BTU Boiler on startup. Draft is good, chimney is clean,works fine while running but on start up when the gas valve opens before the pilot light lights the gas theres a wooosh sound and some flame curls under the front and back of the gas burning area. This presents a dangerous situation cuz the gas valve and wiring is in the area where the flame comes out. first thought is blocked heat passageways through the boiler, but it works fine after startup. problem is worse when the front cover is in place so i am leaving it off for now. pilot light is pretty strong ,tried to turn it down but the adj screw dont seem to make any difference.Gas valve is brand new replacement for original OEM part. Any suggestions as to what may be the problem aregreatly appreciated.