Anyway, today I done the flush and took out the thermostat to check it's not stuck closed and think it looks okay, see below pictures in the open position? I cooked it up a bit and can't wait for the misses to do her nut when she's back!
I also noticed the o-ring is flat and when putting the thermostat back in, it doesn't look like it seats well at all, I did notice round there it looks like it's leaked in the past as there's some pink caking going on.
I'm guessing the second picture is enough to get a new thermostat + o-ring?