Drivers seat heater fan

I have the heated and cooled seats in my 2010MY RR. The cooling function and fan work fine but when I tried the heating functín the fan does not work but the seat does eventually warm up so the peltier cell seems to be working.

Does anyone know if there is a separate fan for the heating function? If there is not then it would seem to be a sensor/electrical software problem ( as the fan works for the cooling).

Any ideas or suggestions to solve this without a main dealer visit gratefully received.