I just suffered from this no heat situation for almost a year. one day i popped off the driver's side panel where the fuses are located, looked in and saw a grey and black electrical connection that wasn't fully connected. So i pushed it in until it clicked and bazinga heat for my entire driver's side

 

Not sure if you've had the chance to do it yet, but I'm facing the exactly same thing. If you look around a bit you'll see that this is a VERY common problem. Cheapest fix is to pull hoses at heater and BACK flush a few times, then fill the heater core with some CLR, let soak, then flush again. With a little air if you can. Then top up system with coolant. This seems to be the fix.