Intermittent and unwanted C5 cooling fan operation

[Richard Stevens]

Possibly related to the non-working fan problem I've been reading.
My C5 1.6HDI fan comes on with water temp showing normal and no fault indication. Seems to be when not driving hard.
Local Citroen dealer could not fault it, and there were no stored faults. I have tried clearing the radiator (and intercooler) with water hose to improve airflow. I suspected the water temp sensor but was talked out of it by the dealer.
Main dealer commented that the sensor was their best seller, so was I right afterall?
Next step to clean relays on the bulkhead?