Whenever an appeal shall be based upon an alleged error of law, it shall be the duty of the board to grant a hearing thereon. The board shall fix a time and place for such hearing, and shall serve notice thereof on all parties in interest.
As soon as may be after such hearing, the board shall either sustain or reverse the referee's award or disallowance of compensation, or make such modification thereof as it shall deem proper.
77 P.S. § 855