Bob,

There is correct voltage to the gas valve at least 80% of the time and
everything performs correctly; it is an intermittent problem. To the
best of my knowledge, though,a reading has ever been checked during an
ignition failure, though.

From what I have learned from knowing almost nothing about furnaces
when this problem started, I strongly suspect that there is a signal
problem between the board and the valve; the board, itself, has been
replaced twice, the valve once. Are there connectors or switches
between the valve and the board?

Thanks for your response. If you think of anything more, I'd really
appreciate hearing about it. It locked out eight times over the
weekend. I'm guessing that number represents almost a third of the
total lockouts since early January.

Bill