can anyone tell me why my windscreen demister is not blowing out hot air?

can anyone tell me why my windscreen demister is not blowing out hot air?

The heater is probably not connected. Check the hoses going into the passenger's side firewall from the engine. If they're not there, there's your problem; and if they're not there, they're probably not there for a reason (core leaking, core pipes broken, etc)

If you're not getting any air at all, its possible your mode cables/actuators or heater control motors are stuffed.

Often when the heater core o rings (or heater core itself) fails, it is cheaper to re-route the heater pipes, and disconnect the heater altogether than to pull out the dash and fix it all.

Does your heater otherwise work? Your op isn't quite what I'd call descriptive, so some more information would help us to determine the issue accurately.

its blowing out hot air everywhere else but the air for windscreen demister is abit weak

Check the cold air pass-through? That does something regarding cold+hot air (I think it might blow cool air through the front vents and hot air through the windscreen vents or something)

where abouts is the cold air pass through located?