hot hair problem

hey guys,

just have a problem in my hot air blower. my Octavia sw has almost 14years and only now I have this hot air problem.

formerly:

- in cold days, I only rotate the temperature switch a bit (less than 1/4) and the fan OFF and the speed of vehicle sent warm air.

- in very cold days, I rotate the temperature switch to almost half and sometimes I put fan in speed 1.

but present day:

- in cold days, I rotate the temperature switch to middle and the fan MUST be at least in speed 1 to blow WARM (not a bit hot or hot), or else it blows cold air.

- In vey cold days, I have to rotate the temperature switch beyond the middle (like almost 3/4) and fan speed 1 or 2.

What could it be? anything broken? dirty? needs cleaning?

thanks in advance