ford ka heater probs?

no hot air entering at normal running temp on idle but when driving air is hot, checked heater valve inlet pipes to matrix they are hot. return pipe is hot but when blower is switched on at idle,air and return pipe go to luke warm/cold has valve packed in, all 4 blower speeds work ok,also looked at the sensor on psg side ft footwell air duct loks ok but what does it control/function within the heating system. t/ stat is ok /no over heating ur thoughts thanks... and yes i have a wet d/side floor pan to, cant find the problem. it rained lots last night and it remain dry ideas anyone and thanks again