Vents blowing out air when off !

Haven't posted in a while since I've had the vrs. I was driving down to Manchester a few days ago and the car started to become really warm as if the heating was turned on, I noticed really hot air blowing from all vents like they was on the number 3 setting.

I decided to turn the heating setting from hot to cold, close all vents and turn the setting to front vents only. It worked but then cold air was still blowing out the feet vent

The more I put my foot down the faster it would start blowing, has any one else had this problem and found a way to get around it or fix it ?

(ps. Got a long drive to essex next weekend and I can't be dealing with heating lol)

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