Nissan Almera radio /heater control panel

Hi All, I hope someone can help me. I have a 06 Almera. There now seems to be an issue with the radio/heater panel. The number 4 on the panel which turns the blast of heating down is not working. It is stuck but all other buttons are working fine.
I was driving last night and the number 4 just stopped working. On the right had side of the radio/heater panel is the heat controller which allows to me increase or decrease the degrees celsius. However when I increase it now, its this big blast that comes out at me and I cant turn the blast down on the number 4 so it is just sort of heating the inside of the car rather than a big blast coming at me. So I have to have it down at the lowest degree celsius to prevent the big blast coming at me.
Anyone have any ideas what the issue might be.