Ford Fiesta heaters blowing cold air

its probably the heater valve thats mounted under the bonnet near the screen it has pipes and an electrical plug to it

Hi your last answer is right,this happend on my daughters car,I posted the same problem and was told by mastertech,its the heater control valve,lift up your bonnet and look at the top of your engine at the bulkhead,you will see two pipes going into the heater control valve ,and two going into your heater matrix,with an electric plug into it,It cost £30 ish,form the main dealer,very easy job to change,took me 15 min,and im rubbish,you will lose a little water,don't worry, This is what I did,put the heater on hot,not the blower, I took the top off my expansion tank,(were you top up your water) started up the car and left on tick over until on running temp,as soon as the air came out I put the cap back on,(please be very careful ,very hot water,don't burn your self,

thanks alot guys i checked the heater valve and the problem is now sorted