Ford KA not known

Hope someone has a clue what im about to ask as im not good at explaining . originally smoke was coming from the area around the ash tray . it smelt like something was melting then found driver side and back seat carpet was wet . from that the car would blow hot air in the car even when ther was now blowers on dash board got very hot .. when i took it to garage they said that a part had broken ... i cant remember the names but they are two pipes that these parts are put into . i know water are fed through these . after having this done car was ok for a few days then omg driving home and steam was coming out from under the bonnet so badly . got home and water for radiator was gone and was like a empty kettle thats been boiled , he has connected the 2 pipes together so i can get to work and he is getting more of these parts but he thought they were damaged parts but when hen removed them them looked melted xx please help i cant keep paying for the same parts i think it is deeper then this and if this is happening to these parts twice now what could be causing that xxxxx thanks