Maxwell Malinois

Got a 2011 Legacy about a month ago and it has no heat at all on the passenger side. Brought it to the mechanic, they flushed the heater core which made the heat on the driver side hotter, but the passenger side is no longer ice cold but not hot.. I'm wondering if it's just not been back flushed or if it's got a blend door problem or something. Any thoughts are appreciated.