Fan relay issue HELP!!

Hi

I have a 2000 model 1.8T 180BHP model on an X plate - the fan did not cut in beforewhen the car reached 90c and it went over - my mechanic replaced the relay ashe said that there was a signal going into the old unit but nothing coming outof it - The new unit I replaced with is (Part number: 1J0 919 506 K) a new partI bought off eBay - no markings on the new relay) it works but the fanconstantly now remains on! My mechanic says that it could be the temperaturesensor in theory that is at fault as the sensor is thinking the car is overheatingwhen it is not - so he is ordering a new temp sensor - has anyone had a similar problemand got it fixed? The part has 14 pins (Part number: 1J0 919 506 K) as Audi didsay that for that model it came with 16 or 14 pins - so it is definitely 14pins. Both the front fans work. The car has a very recent cambelt and water pumpchange So my concern is will the temperature switch beingreplaced solve the problem or will I need another fan relay?

Thanks