It'll be the actuator, or control rod.
Worse case is it'll need to entire heatbox replacing - About £75-£200 for it used, and front doors off and dash out to remove and refit (took me 13 hours on a friends Panda).
Not something for the light hearted and not going to be cheap on labour if a garage doing it.
Yeah I hope it's not the entire thing.
Is the actuator the one on the left?
Anyway to test that it's working?
Thanks.