Strange heater blower behavior

[TonyErwood]

The heater blower on my 2012 XTR goes to full speed for 5 seconds and then stop for 8 seconds and this cycle repeats continuously while the engine is running. It is possible to stop this cycling only by setting the blower speed to zero. The heater controls otherwise seem to behave as normal with heating and cooling following the temperature set for the left and right sides.

Any ideas on what might be wrong and how to correct it would be much appreciated.

Tony.
Shetland Islands.

P.S.  We no longer have a Citroen dealer in Shetland.