Check the water level and top up if required.
Next check that there isnt any air in the heater matrix.
To do this locate the two heater pipes at the rear of the engine that go into the bulk head of the car. One of these pipes has a small thumb screw on it. With the engine running, loosen the screw to allow any air out and re tighten. Recheck the water level and run engine up to temp. Hopefully this will have sorted the problem. Beware...if regular topping up is required or you some times hear running water in the passenger foot well whilst reving the engine this may be an indication that the head gasket has failed. Common fault on 206.
Macca
April 2011