Coolant temp sensor.

[Bravo]

Good afternoon,
I have a 2009 Astra 1.6 z16xer I believe. I recently got the spanner warning light and after doing the pedal test got the fault code 218217.
There is lots of posts all over the internet regarding the cure from replacing the coolant temp sensor on the bottom of the radiator to replacing the plug connector too.
If I replace the sensor and or the plug connector will I have to have the car plugged into a diagnostic reader to have the light reset or will the car's ecu see that the fault has been rectified and reset the light its self.
I was also wondering if it was worth replacing the thermostat too as it looks like there's also some sort of sensor on the housing body.
Any help would be gratefully appreciated.

[Bravo]

Hi there just wondering if you could shed some light...