i have a FMI direct vent fireplace about 15 years old. it has always worked well except for this year, the main flame keeps going out. Sometimes it will run for up to 10 mins and then go out....sometimes it will not even light. i replaced the thermopile (power-pile) but that didn't help. The pilot stays lit no problem. I have cleaned off the contacts and snugged things up but no luck. Before i spend $200 on a new gas valve (SIT 820 nova) is there anything else i can try?

thanks