Purchased and installed a nice set of unvented natural gas logs last year. Fired right up, worked just fine all last winter. Cut off pilot last spring. Tried to fire it up this past weekend, pilot lights and stays lit, but main burners will not come on. Took it out of fireplace twice, cleaned all thermocouple surfaces, sprayed compressed air into main burner tubes, checked wiring for loose connections, but main burners will not come on. Manufacturer help line difficult/impossible to get through to, and manual with gas logs not much help. I can't believe that it is anything all that complicated, but if anyone can suggest other items to check, it would be appreciated.