In the timed cycle, the moisture sensor circuit is out of the loop.
Other posters suggest that you look at the thermostats. Well, it is
highly unlikely that the stats are your problem. Think about it: a
thermostat just doesn't wake up one day and decide that he will stop
working at 100 degrees instead of 165. It either works or doesn't.

I would suggest that the coils on the valve are your culprit. There
are two. Replace them both. There should be a bracket that holds
them to the valve. Remove the bracket, and the coils come off
freely. But, if you have a really old style of burner where the coils
and wiring are integrated and hard to remove, you'll need to change
out the whole assembly.