The way your comment is worded is perfectly fine. In fact, it has been previously covered by Marco Ceppi:
As for nudging the user, there is nothing wrong with leaving a comment on the question requesting the author select an answer - or improve their original question if it's still unanswered.
Not every single new user on the site knows how Ask Ubuntu works, so giving the user suggestion ( and only a suggestion, not direct push as in "Accept mine and only mine" ) is perfectly ok.
In addition, accepting an answer is a way of communicating to others ( from OP's perspective ): "Yup, that's the thing I was looking for". It doesn't necessarily imply that it works in all cases - just for that specific person. They can sure leave an answer unaccepted to signify that the solution didn't work in their case. But when OP says "That worked ! Thanks!" , I personally see accepting an answer as way of ( at least visually ) confirming the solution works
