BMW 316i SE Auto
I get a fishy smell coming throught the windscreen, footwell vents etc when I turn the heater on. Also get masses of condensation which "steams" out through the vents. Does any one know what the problem might be? I beleive it might be a problem with the heater matrix core. Could it be anything else? and what sort of price for repair??

Probably a mold issue on the evaporator core. The are spray products that will disinfect and deoderize the ducts. Some cars are accessible through the blower motor opening.