same problem a few months back and was very easy to fix.The heater resistor has packed in,it is located behind the glove box just follow these steps
1,Remove the two 8mm bolts underneath the glove box and pop it out
2,You will see the resistor (coils covered in flux)
3,Remove two screws using a stumpy philips head screw driver
4,Replace with new one in the reverse order as above
New one cost about 30 quid
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