I've tried the suggestions and have come back with the following:
The CPU is running around 53 degrees idle
The GPU is running around 47 degrees idle
The films do work on my seperate monitor.
I changed the TV setting to Cinema mode as directed by support (it was also in the manual
After playing around with various settings on the TV, on the Nvidia CP, codecs etc and pulling my hair out, I've found that leaving the Nvidia settings to 1080p 60Hz resolved all my issues!!
I hope this is the last of it!!
Thanks for all your help guys.