Fan is off but hot air is blowing from windscreen vents

Whilst driving the car is becoming really hot, i noticed hot air is blowing from the windscreen vents -even though the fan is on 0. Its quite unbearable.

That is a sign that your heater control valve isn't fully closed, or that in the afternoon with the sun beating on the hood it will be hotter than normal air off the hood into the blower motor.

With the blower motor on 0 you will get no fan movement but you can have flow through ram air in to the system and it will push air out.  Your side vents on the Dash should be non-heated air or a different temp, than the defrosters (demisters).

It is usually caused by the heater control valve and cable assembly not being fully closed. You can remove the clip and reposition the cable assembly…It could also be that your heater valve is broken internally and that it is fully open when it shows closed (had that happen).

If you find the valve is bad, then you may want to use the Porsche Valve as it is the same size and more like the original Vane type of the early rabbits and not the barrel type that they sell with the same part number.

See: View topic: A Porsche replacement heater valve - The Mk1 Golf Owners Club

Air still comes through when moving even with the blower turned off but I guess your heater water valve is faulty or nor adjusted properly as Briano1234 says if the air is always hot.
It's normal for air to get in and either hot or cold air to come out of the vents as it helps with air flow in the car.

If you put the heater direction controls to the middle it should stop any air getting to the windscreen or your feet but you need to check the valve as it's not normal for hot air to get in.

You can remove the valve and see if you can blow through when it should be closed, I had to change mine this year as my car would not blow cold air.

https://www.ebay.co.uk/itm/Heater-Control-Valve-for-Heat-Exchanger-VW-Golf-MK1-Caddy-1-Cabriolet-155/311930885143?hash=item48a0879417:g:jyMAAOSw-olaDJVu

Thank you guys. I can see if i move the control unit to close and open it does move.

But it could be that it doesnt close properly? Hoow do i remove this valve?

Also is there anything else i should check where the heater controls are? (Under the radio?) Thanks

If you are blowing hot air out of the defroster / demister center vents or side, it is usually the heater valve that isn't fully closed.

The controller in the center of the console controls the heater valve via a cable.  

The heater Valve under the hood can break internally and be closed when opened, or the other way.

I would validate that the heater valve is fully closed.

When the car is cold as in first start the air is cooler that blows over the hood and into the intake.  They used flow through ventilation on the thing so with out a/c which has a intake flap to close off the under hood air you have a direct flow of air.  

The air under the hood and over the hood after running and stop will heat up and be hotter than the ambient air outside.  

So if you are having hot air, then you should look at the heater valve….

Hot air isn't a function of the controller (ok the hot/cold) air lever, but if you have it on cold, then you should have a tad bit warmer air than outside.  If not then you have a bad heater valve, or that the cable isn't adjusted properly.

The heater valve was faulty also the clip for the wire on the heater control panel was broken. It's all working fine now! Thanks guys