Overheating, throwing water out of cooling system, possibly heater not working..

Solution. Cold engine. Set heater valves to full on.Undo radiator cap. Go round squeezing all hoses., open any bleed screws (if any), Hopefully you will lower level of water in radiator as air bubbles are moved. Top up with antifreeze mix. Continue. Then start engine and run for 5 minutes. Repeat..

If really bad you may have to drain entire system and SLOWLY refill possibly using a sealed feed into radiator from above the radiator to remove airlocks...