I called ESW support this morning because I was curious about this.
They said that for my 2008 25-PDV the default mode is actually 'D'.
I see from the OP's signature that the stove in question may be a 2011 and I don't know if the same applies, but it would be worth calling ESW support to verify. I've called them a handful of times and while you might be on a hold a little while (since it is the heating season) they have always been extremely friendly and made sure all my questions were answered before they hung up.
They really intend for owners of their stoves to call support if there are any questions, so you may as well use the great service they offer! That is one of the reasons I ended up buying my stove from them
.