No hot air!

[Greg66]

I've got a FL 4.2 Q Sport. Slightly odd ventilation problem. No hot air.

Normally if I start the car from cold the fans won't start to blow warm air until the engine is producing warm air - then the vents will come to life and the fan speed picks up. As of last week though the fan speed stays resolutely on one bar, no matter what temp I select (with the exception of LO - then it blows a gale and won't stop blowing a gale until the engine is switched off and on again).

So, a flap - I guess - is staying closed and diverting hot air from the engine bay away from the cabin. The question is whether the motor that opens the flap is done in or whether a sensor in the cabin is done in.

Has anyone experienced anything similar, and if so, can they offer a ballpark cost to remedy?

TIA