2000 Ford Fiesta heater not getting hot changed control valve and flushed matrix

you have a air lock in the system run the car up to tempreture and have the heater controls on hot and the interior dial to screen and just get the engine hot and keep a eye on the water level and top up when the level dropps but be careful when you do this as the water will be very hot and under pressure so be careful do this and let the car cooling fan kick in at least 3 times to be sure that all water is flowing properly around the system

is the engine getting up to operating temp as these vehicles do not tend to air lock, check that the thermostat is not stuck open.