Hurray !, my temp is now working, I am pretty certain now that this is a software glitch of some kind that doesn't seem to fix itself on downgrade, as I know when you downgrade the firmware a lot of the settings are still there. Anyway, I tried a kty84, kty83 (which comes with the controller), nxt 10k (which comes with the cromotor) and after firmware upgrade none of them work, so iv been on eBay and bought every sensor known to man, I know the controller has a kty83 or 81 in it so decided to get a kty81/210 as listed here http://www.ebay.co.uk/itm/271444888840
and as soon as I plugged that in I was getting temp readings of 172 degrees c , (because I had it set to kty84 in the settings), I went into the settings and changed it to kty81 and then put my head gun on it to warm it up and the temp actually rose!.
So now I just need to tear down my motor yet again and replace the sensor, hopefully for the last time. By the way, anyone that wants to test sensor, you don't need to tear down your motor to do it, just unscrew the halls connector, and insert the sensor legs into ground and sensor inputs (note they are a mirror image to the ones in the manual as its the opposite side), then just warm up the sensor with a heat gun (not too hot though, I set mine to 100 degrees), and then watch the screen, if its going to work it will rise as its heated.