1999 Ford Fiesta heater

Check heater control valve .

agree with whitinghame,heater valve is very common fault

I have a 1999 Ford Fiesta Ghia and I'm at my wits end on how to solve the heater problem I have had for the last 2 or 3 years. At one time the heater would not work at all and it was Winter, a 'friend' replaced the heater control valve with a new one I bought on the internet and it worked for about an hour. I ordered another one from a different vendor on the internet and whilst installing it found the reason for the failure of the first one. A piece of the plastic from the first HCV had lodged its self inside the new HCV. But the HCV seemed to be working because it was nice and hot, it was Winter and when summer came I found that the heater was blowing hot air all the time. I replaced the HCV with a new part from a local supplier, no difference, got a garage to change the thermostat, at great expense, no change. I then replaced the electronic control board I got 2nd hand from a newish car that was being scrapped, still blowing hot air. Checked with a local garage and they said the fault MUST be the HCV and I MUST fit a Ford one as other makes did not work. I popped along to the Ford Dealer and when I told him everything I had changed he said it cannot be the HCV, maybe the heater matrix is blocked, try investigating that. He would sell me a Ford HCV at £54 but I could not return it if replacing it did not cure the fault. Can anyone suggest how to fix a heater matrix blockage please ? I tried attaching a hose to the HCV but the water seemed to be going in one side and coming straight back out the other without going through the matrix. I'm really stumped, can anyone help ? Dan in Port Glasgow.