Heater problem

[seatrip]

Hi some help would be greatly appreciated please.
I drive an 08 leon essence...been a troublefree car since I got it. Yesterday I noticed that the heater started blowing cold air after about 15 mins driving but if I turned it up full it was really hot again. Same thing today, after initial heat-up it only has two choices cold or maximum heat. Anyone any ideas what could be wrong?

[Jempe1012]

I also have this same problem with my 08 plate Leon if I set the temp to 29.5 it's cold if I set it to HI it's red hot there no happy medium with it really annoying me now any help with this problem would be great

Cheers