I agree with previous posts and check connections on the board, over yrs and especially on out door gas appliances low voltage spade connectors can appear to be tight but build up deposits which creates resistance/problems with boards.(just push in/out the connectors 3 or 4 times which will scrape the male terminal and make better contact, also if you can "gently" squish the spade connector with some pliers, that helps make better contact also) Also check the ground spade connectors, Many boards check flame signal via the ground connections.
also may be a bad board...
good luck
Mike
