Peugeot 306 XTDi Passenger Heatwers don't work?

The coolant level ran low and whilst this didn't have an adverse affect on the engine cooling (the fans kick in and do a good job) when I re-filled the car with the correct anti-freeze and water mix and ran the car plus radiators on hot and full to hopefully elimante air locks this has had no affect. The temperature runs at around 70 degrees C around town and on the motorway. I have twice re-tried taking off the radiator cap and running the engine / heater to now avail. Does this car have some sort of valve as part of the heating system that could have stuck?