Ford KA heater only blowing out cold air

check heater electric control valve witch controls hot water from engine to cabin usually found on bulkhead area under bonnet

Heater control valve common fault on these,open bonnet and look at the centre of the bulkhead at rear of engine compartment you will see 2 water pipes going onto it you will have to unscrew some of the plastic panels to get acess to it unplug multi plug and 4 hoses u can buy these from fords they are not that expensive also ebay sell them etc,remember change when engine cold(just to check this is fault feel the water pipe going into the valve when engine hot to see if pipe water is circulating to valve)