P38 heater blows too hot or too cold

hi,
does anyone have any suggestion on what the problem could be with my P38 1996?
the temperature will not stay at a good level. i put control to 'low' and it will blow cold air. when i put it to '16' or any higher it sends through very hot air? it is becoming very annoying!
any advise would be gratefully received!
cheers
gredders

have ya tried any position in between?
don't turn it up to 16 and see what happens, try 15 for a while.

lowest it goes to is 16 then down to low! thanks for having a go anyway!