Ok, now I don't really understand.
On the very code I pasted in the last post, I changed the ventilation from 30seconds to 40seconds to see if the start sequence would then stop on it's own...
It appears that if I put 40seconds to ventilation time, neither stops. Not the starting sequence nor the ventilation sequence.
And of course if I set it back to 30seconds, I do have the ventilation stopping and the start sequence not stopping (as before).
