your heater system may have an airlok near the battery under the bonnet you will see 2 pipes going into the bulkhead fibre stuff above one of them it will have a bleed screw u need to warm the car up 1st and leave it running, undo the nipple and let some of the air out, it water is just comming out then your system may be blocked and need flushing out, if so just take the top hose of the radiator and stick the hosepipe down it and seal with your hands then put the tap on full blast and wait for thewater to become clear whats comming out of the radiator.